If you are interested in playing now you might be able to borrow a codex from someone. It isn't something I would suggest buying until the new one gets out. At least that will save you some money for beer in the meantime.
You need your standard HQ, 2 troops and what ever vehicles you want to start with.
I've totally gone through the same decision making process myself and I ultimately came to the reasoning that basic riflemen and the standard issue "nothing special, vanilla flavored" troop squads would be something that never goes out of style. it might offer you a way to start.
welcome back, however! if we can help at all, let us know how and we'll do our utmost.
Pipe down Sergeant, we'll be back on Cadia before the 14th black crusade, afterall, that heretic filth woudn't dare show up until we arrived after the bootstompin' we gave em last time!