Paul, do you want do "paint" as in solid colors? If so I can't help much - that is the realm of auto paint. I have a very good friend who paints custom motorcyles - somebody like that could coach you.
If you want do do "finishes" as in clear or tinted or even sunbursts, then I can share my learning experiences. My first couple of guitars were done with rattle cans of lacquer - I thought quite acceptable but like you I wanted to move to the next level. I am still learning and experimenting, but here is what I've done so far.
I found a small home air compressor at a yard sale ($50), I think it is 2hp and 8 gal tank. I added a water filter and pressure regulator. I started with a siphon "jamb" gun (about 4 oz) but have moved to a gravity feed LPHV (low pressure high volume) gun that I bought at an auto parts store. I added a pressure gauge at the gun.
This has allowed me to experiment with both nitrocellulose and so called "water born" lacquers - frankly both have advantages and disadvantages.
Nitro is easy to shoot and get good results, but it is hazardous, explosive, and a bit of a hassle to clean up. I don't have a spray booth (actually I could go to my motorcycle painter friend) but I shoot outside on warm days with moderate humidity. I wear a full respirator. Clean up involves taking the gun apart and cleaning everything in lacquer thinner. I can add dye to lacquer and do tinted, shaded or sunbursts. These are finished in nitro
Water born lacquer (I've used both StewMac's and KTM-9) is not toxic or explosive, cleans up with warm water and seems to give a very nice finish. I have tried tinting and shading it with good results. These were finished in KTM-9
A potential problem with the water born finish is that each coat does not melt into the previous one like nitro and you can get "witness lines" when you sand.
My point is that once you have committed to an air compressor and small gun you can try many different finishes (including automotive, I just can't tell you what). Some sort of spray booth is advisable, particularly if you want to finish in doors. Dan Erlewine's book on guitar finishing (StewMac) is highly recommended, and as always, practice on scrap.