Yes, and yes, although not necessarily in that order (for MVS at least) :P
Search for Neo Geo development manual using the Googles, and you will find what you seek (and also visit the Neo Geo Dev Wiki).
Vasm for code, MAME debugger build for... debugging.
It's a seriously weird system, basically everything you see is a sprite (including backgrounds in games, etc) - quite different to most console/arcade h/w - but then that's the fun
