Paint whole or take apart

It kinda depends on the paint. If it's got a metallic content, I like to do the final paint all assembled- since the metallic can lay out differently if sprayed piecemeal and it can be noticeable when assembled. Pearls can act the same way.
When the car is disassembled, I'll shoot the doorjambs, trunk, engine bay, door edges and underside of the hood and trunk lid and inside of the fenders (and bottom of the car if on a rotisserie), along with any loose parts (hood, trunk, and door hinges, for example).
Then reassemble the body, and do final paint prep.
Then shoot the entire exterior at once, hopefully ending up with a uniform finish. (that means all my watermelon stripes line up...!)
With solid colors I can get away with painting it all piecemeal and assembling it.
Just my way, and I'm far from an expert.