thats for primer! i have one of those
You can use it for whatever you want as long as you have the appropriate air cap and tips on,
I use two GTis day in day out, One for base and the other for laquer and an old sata for primer, 1.3tip on the base and primer and 1.4 in my laquer, also have a small sata gun for wheels but it doesnt get used very often at all, Only unless i've a few wheels to do at the same time as having a different colour on my GTis it gets used
Wouldnt bother with an SRi if you are painting the car, they are ok for small jobs such as wingmirrors and wheels but no good for painting anything bigger TBH.
A gravity fed gun is what you are after, If you can get a bag system great as it'l allow you to paint with your gun at all sorts of angles if you can stretch to PPS system is better and is what we use at work they have filters in the tops so you dont have to prick about doing that either!
Its quite expensive to get set up so if you're only doing a one off job i would pay to have it done