Yeah I just use pdfs/Battlescribe for my necrons and DA, but I bought her a used Tyranid codex so she has something tangible to absorb. All she has right now unit wise are some used/primed genestealers that she needs to paint and used well prepainted Carnifex and special Broodlord I got a deal on (were from the Blood Angel/Tyranid boxset). She's not quite ready to actually play yet but I told her to read on the synapse thing. Hard to find used deals on the good tyranid units like flyrants, raveners, and mawlocs. I'm keeping my eye out though.
Nids also need a new codex. GW is moving in the direction of formations vs CAD, and newer codices have formations. Necrons, SM, DA, Tau at a minimum have formations in their codices (not sure off the top of my head about others). Some supplemental books have formations, both for factions that already have some and those that don't (For example, Mont'ka has Tau and AM [guard] formations. Not sure if it has any other). There are some Tyranid formations out there at least from the Exterminatus supplement and the Blood Angel/Tyranid box iirc.
Formations are alternative army structures to the CAD which confer additional benefits to the member units. Newer codices provide the faction a massive overarching Detachment option comprised of a core formation plus numerous optional auxiliary formations. the Core formation will have it's own bonus, as will the minimum single auxiliary of your choice. This will get you the overarching Detachment bonus, which extends to all formations within the detachment, on top of each respective formation bonus.
http://bloodofkittens.com/formation-compendium-2/
Has most formations. The problem for old codex forces is that to be "Battleforged" you have to run the minimum CAD with no buffs, and then take appropriate formations which don't run against CAD limitations. Of course if you only play casual you can simply houserule all legit formations within a single faction be battleforged rather than "Unbound". (This is all 7th edition stuff afaik). The importance of this is being Objective Secured. "Battleforged" armies get OS, but Unbound armies don't. In other words, if you are Unbound and your opponent is Battleforged, "Contested" objectives are not contested, the Battleforged army has them.
Edit: I'm pretty much done with my own stable of factions: DA for a MEQ army, Guard because tanks, and Necrons because lolnoimnotdead. I am working on some Inquisition/GK stuff to ally with Guard, but I don't intend to ever stand that up on its own. I originally messed with DA as an ally for guard but they just don't work as well as I think Inquisition/GK will, plus DA is one of the cheapest SM factions to get into. Plus bikes. Plus Deathwing.
