In my opinion you need to do some paint work first. But not all.
Unless you're building this into a rat rod and leaving it in primer forever (doubtful), IMO you gotta paint the full unibody now (skipping outside of quarters, pillars and roof if you want), and the inners/edges of every body panel, door jambs, inner pillars, underside of hood/decklid, etc. In short, you need to paint every last painted portion of the car that is going to be covered up by something. This is because it is simply not possible for you to properly paint a part later, that has already had parts bolted and attached to it.
If you took it this far, don't start skipping steps now or you'll hate yourself. And your friend that is helping you with the final refinish will hate you even more. It is time to paint first. Basically paint everything that will be hidden...so you can skip all the outer surfaces if you want your friend to do all that later. Then you can assemble the car, excluding trim, lamps, bumpers, and moldings. At that time it is your choice on how far you want to go into the final metal work/block & prime process for the final exterior refinish, to reach your chosen level of perfection in body panel alignment. Then your final exterior trim gets bolted on last.
At the very least, talk to your buddy who is going to help you with the refinish, and develop an agreed plan before going any further. He may make you undo a bunch of stuff you want to do now...
