Car painting guru's, please help noob paint camper shell

I'm mechanically inclined, ASE master tech, Mechanical engineer etc. and comfortable turning a wrench but have never sprayed anything I really cared about with paint and clear coat.
I bought a camper shell that's the wrong color (black) and I want to paint it to match my truck (magnetic gray metallic) but don't want to spend a bunch of money on supplies, prep and make the shell look even worse by a crappy paint job.
Where would be the best place to get the paint?
How do I know how much to "thin" it?
How do I know how many coats to put on?
How do I know how much paint to buy?
Do I sand or finish the paint in any way before spraying clear coat?
Same questions as above for the clear coat.

I'm sure I'm overthinking this to some degree but I want to do it the right way. Please don't reply and tell me to take it to a body shop, Maaco or whatever. Only reply if you have relevant experience and are willing to point me in the right direction.
Thanks in advance!

 

Lot of things depend on the paint itself and what the manufacturer suggests. No general rules, or not many anyway. Do you have a local automotive paint supply house where you live? That will be a great resource for the stuff you want answers to. If not, we will see what we can't steer you a bit.