Ok, the first question is are you doing Tempestus Book or Militarum book. Note that from now on Scion = Stormtroopers and Astra Militarm = Imperial Guard or IG
I will explain as if you are using them as part of a main IG force. Note that even in this situation it is generally better take them as allies because the orders in the Stormtrooper codex are better suited for them. That said, you would need another model to do that or a commissar to act as the HQ choice in the Stormtrooper book. Get another box of stormtroopers or buy the remaining model from a bit seller. Right now, I would build them with 4 Lasguns, one laspitol CCW, 2 melta, 2 Volley or plasma.
When using them in the IG, you have to compare them to Veterans and understand what they do better. 9/10 times Veterans should be your go too unit instead of stormtroopers. When ever you pick unit in the IG book you need to pick them with a task in mind. Veterans are a line unit that can also serve as a special weapon platform or a back field objective camper. Stormtroopers are just specialist unit because they are too expensive otherwise.
To explain this further (if you don't care skip to the next paragraph) Carapace Armor Veterans (gain through the grenediers doctrine) are five points more than the Stormtroopers. The different then becomes krak grenades and the hot-shot lasgun verse 5 extra bodies. With T3 both units are going to be wounded on a 3 or more dice roll. You will find that means most of the time you will be rolling for a lot of saves verse nearly ever weapon in the game. In addition, most special weapons ignore the armor save and those that don't it is only a 50% you will pass. In short, both Stormtroopers are Carapace Veterans are easy to remove from the board. The extra bodies in the Veteran squad go a long way in them sticking around. As for the lasguns, the hot-shot lasgun looks great, but in practice it struggles verse most units. Most enemy armies that have 3+ saves usually also have T4 meaning you just are not generating the amount of wounds you need to be effective. Mathamatically, the hot-shot is a little strong than a standard bolter. It good, but not great. In addition, the 5 extra shots from the lasguns kind of level the playing field between the two weapons. Especially since it is easier to get into rapid fire with the regular lasguns. The hot shots will barely score more wounds. Then you add in the fact that the Veterans can take a third special weapon. This is pretty huge because as previously stated you build usings in IG with a goal in mind and you take Veterans for the special weapon slots. The krak grenades Stormtroopers get standards are kind of moot, it is an bonus stormtroopers have, but in most cases if you are charging with your guardsmen you have screwed something up.
So why take Stormtroopers at all? Deep Strike! Never take Stormtroopers in transports always deep strike them (like 99% of the time). If you are bringing a unit transports take Veterans because of the reasons previously stated because they are better at that. Deep Strike lets you appear anywhere and solve a problem as the game develops. In 7th edition, mobility or the ability to reach objectives quickly is the name of the game. The updated Guard book lost a lot of that mobility. In addition, Stormtroopers get move through cover so they doesn't take penalties for landing in terrain. Deep striking is a huge advantage that most people don't utilize. The reason it is not more popular is because in can be unpredictable. The internet will tell you this is bad especially in a tournament environment. However, as a new player that should not be an issue. The main disadvantage to deep striking is it leaves you troopers vulnerable to a assault. The trick is getting close enough to do your work and far enough away to give yourself some hope to survival. Or to just in and be ready to die.
There are a couple main builds for the unit. Here is what you should lean towards and stay away from:
5 man 2 x Melta Suicide unit - This one is a vehicle killer. Deep strike you guys behind a key unit and hit it in the butt with meltas. It is very effect at eliminating problem units that have gotten out of control. They will probably die soon after. However, one their target is dead it no longer matters. It is important to understand that sometimes trading points for points of models is okay.
5 man 2 x Plasma Suicide unit - In the same vein, this is a good unit to use to take out expensive elite infantry. This is really good for things like devastators or obliterators. Any time where your opponent hides powerful units in the back field and is just annoying with them.
5 man 2xFlamer Suicide unit - In this case are counting on the Stormtroopers to deep strike in close and burn a horde to death that is hiding in cover. This build is decent for doing that job, however the short range of the flamer kind of hampers it. In addition, there are usually better ways to do this in the IG book (Wyverns). Some people like it, but I would steer clear.
5 man 2x Grenade Launchers - Don't take this. Grenade Launcher are not very good and it does not sync at all with the hot-shot lasgun. By sync I mean their range and prefered target or off. If you take GL use them on infantry squads.
5 man 2x Volley Gun - Ok, but avoid I will explain why further down in a paragraph about the volley gun.
10 man squad - This is a pretty good unit when partnered with a command squad in the stormtrooper codex. The stormtrooper codex has some orders that really help them out. When you give the entire squad rending at a target or sniper suddnely they become pretty great at killing Monstrous Creatures or other difficult targets.
10 man squad x 2 plasma - This is like the previous however, it is has a little more sting. I would still stay away from 10 man squad without access to orders from either the Stormtrooper book or IG senior officer orders.
Now we will discuss the Volley gun, the Command Squad, and the Taurox Prime.
First the Volley gun. One paper it looks great, but it is really not designed to be used by Stormtroopers. The salvo rule means if they move or if they have deep struck they range is cut in half and so is the amount of shots. As previously stated, you are almost always deep striking. The problem with this is it means for one turn you are going to be hamstrung regardless. For this reason it is not really suited for a regular squad because they need to get in close with their regular hot-shots and to be expendable. However, on a Command Squad the story is changed.
The Command Squad is pretty essential (serious get another box and a replacement 10th model). The first advantage is orders. Being able to DS in a unit with IG orders is awesome. In the IG book, you have access to two great orders that works well with the Stormies. First Rank Second Rank Fire is the damage increaser and a no brainer. The other is Forward Unto the Emperor. This is great for moving you guys out of harms way or onto a vacated objective. Another advantage is they can order your other nearby squads. It is pretty sweet. Things get really crazy though when you get the Stormtrooper book. The orders in there are pretty great for and really increase the effectiveness your squads. The disadvantage is you can no longer order IG units, but that is a small price to pay. If you end up going for a ten man squad you need at least one command squad.
The second advantage of the Command Squad is the ability to take 4 special weapons or 3 and a medic. Before that I will say don't take a standard or a vox. The standard is going to be wasted because in general you are going to get wiped out in CC. The extra point for resolution is going to be wasted. The vox is tricky because it seems okay, but the fact is none of the orders are so key that you need to pay 5 per unit for a reroll. It is only really worth it for senior officers on key units. The medic is a decent upgrade on the right unit. If you are going up close and personal avoid it, however at a distance in cover it can be a solid upgrade to keep a key built unit alive.
Here are some builds:
4 X Melta - Like its buddy up top but more powerful. This is a great unit to have especially in the stormtrooper book. They have a preferred enemy order that mean you are nearly 83% chance to hit with those meltas while also ensuring a wound or hit is delivered to the target. In the IG book it is still great, but not as strong.
4 x Plasma - Again same as above. Preferred Enemy order is great.
4 x Flamer - There are better ways to get four flamers in. I would avoid.
4 x Grenade Launcher - Don't take this ever - see above
4 x Volley Gun or 3 Volley Gun and Medic - This is a pretty great squad. Once set up you can lay down a punishing amount of fire power. 12 to 16 S4 AP 3 shot is huge. That is an insane amount of fire power. Combined with the Stormtrooper twin-linked order and you have a serious MEQ killing unit. Because of the distance you can operate at the medic can really do some good work keeping you alive especilly if you find cover to hide in. The main downfall is the set up. You have to get to deploy. That means either deep striking in or taking a transport (this is the one time I where you could do it and it is still probably a bad idea). The other option is to leave it in place and use it as area denial. Anyone that strays within range will be ripped to shreds by the fire power. It can be great behind a gunline.
Last thing, I will mention is the Taurox Prime. The Prime is a weird one. The problem is that it is too expensive for what it does. A lot of people underestimate the regular Taurox. It is proving better than most believed. The issue is that it is still easy to kill a Chimera if you want to and the twin-linked autocannon is a great weapon to have. In addition, the free reroll terrain lets you drop it deep in ruins for a solid save. Theoretically the same thing applies to the Prime. However, that is a big risk. It is easy to kill if someone really wants to. And because you are sinking point into the vehicle it becomes a tempting target. The upgrades are not so great as well, fast is nice but the weapons are questionable. However, if you like taking them just because you are deep striking doesn't mean you can just buy and use the empty transport.
I hope that answers your questions and maybe helps you out. Let us know if you have more.
