I'm at this point too and I've been giving it a lot of thought. I have all the construction done except the canopy. I'm ready for the avionics.
I've gone the rattle can route and it wasn't very durable although I didn't try appliance paint. I admit that touch up is a breeze. However, I found a company in CA that can put any paint color in a spray can so that kind of negates that benefit.
I think I'm going to fly with just the cushions installed and the interior bare aluminum until I fly the 5 hours off. Then I plan to build my own custom interior using skins that Abby is sending to me. I just have to do something to make my -12 unique in some way.
Also, just my opinion, I don't think priming the entire interior is worth it. I doubt the actual corrosion protection it might provide and if most is covered by carpet and interior panels, I don't want to add the weight. I admit it's not much weight, but then I feel I need to keep it looking nice. Bare aluminum is much easier.
For the exposed areas, I will probably mask, prime, and paint them a color to match my interior. That will include the inside of the canopy, sills, roll over structure, main spar area, and seat backs. The rest will be covered. That's not much to paint so masking shouldn't be real tough. Am I missing any other exposed areas?
That's the plan so far subject to change.