depends on the tuner what an exact stage means, but head work involves porting and polishing the head, usually fitting bigger valves & better guides. Just allows more freeflow, 8v head is stupidly restricting.

a head is usually specced to your turbo etc. If you know what you want the car doesn't have to be off the road long, a good idea would be to talk to a tuner NMS, Jampsport, Motorsport Developments etc they'l discuss what you're after performance wise and once booked in should have ot done pretty quickly.