OK- as for prep, there are a few questions-
You say your buddy will shoot it if you can get it???
Am I assuming you're wanting to use an over the counter DIY product?
If so, there's not much I can tell you except follow the label. I've yet to see one that I would pay money for, but I'm a little prejudice. The Herculiner is great for the money for trim areas and tub linings, but I truly believe it would look like hammered sh*# if you tried to do the whole thing. Also, the color (if you could even get the color you wanted) will not hold up.
The product I use can't be "sprayed by a buddy" It's a two part system that is heated to 170deg, and pressurized to about 2500psi. It requires specialized equipment and training.
I always get asked what the customer can do to save himself some money. On a complete, about the only thing is disassembly. The masking requires specialized tapes and positioning (you'll want your doors to open and close and your windows to roll up and down), so I'll usually tell people it's gonna cost more if they start fiddling with it.
One thing to warn you about-
I don't know if you care or not, but even if you use a reputable shop to have this professionally done, you will lower your resale value. It really only appeals to a very select few.