This has been answered pretty well by the above posters. However, I'd suggest picking up a copy of Soul Hunter and give it a read. It does an excellent job of describing post-Heresy traitor legion whatnots. It specifically talks about repairing equipment, recruitment, wargear, etc. Granted, not all legions will be the same, but it does give a pretty good showcase.
Profit Factor - my RT blog
The corruption of the space marines is a risk that is now as real as it was during the Horus Heresy. The novels tell stories of corruption of space marines from the Dark Angels, Blood Angels, and so on. In the Eye of Terror novel, they even describe the whole ritual for this corruption. Clonning space marines is also an myth usually told. It is even said that Abaddon the Despoiler, form the Dark Legion, is a clone from Horus himself.
Have fun and keep rolling!!!
"Sanity is for the weak!"
WIZARD OF OZ