Painting Advise

Okay I've gone around my whole body of my Model A with shortstrand fiber filler, then I went back and skimmed a layer of evercoat glaze over every panel from the beltline down. I blocked everything out, sprayed on a guidecoat and blocked again with 180 grit to finish. I don't think I could get it any better so that's as far as I want to go for now.
I'm wondering now how I should go about the next steps.

One, I have to cut a big hole in the roof to put in my sliding ragtop and I would like to have it bolted to the chassis so it doesn't run the risk of twisting. It's very solid but it makes me wonder if it could be a problem.

Two, I have to do some more filling above the belt line.

Three, I have to prime, block, and paint.

I was thinking I should finish it up until all the sanding is done, paint the firewall and then mount it on the chassis. Then cut the hole, mount the frame for the top (then take it off again) and then paint the body on the chassis. Any other ideas, do you think I would be okay to do the top off the body then just do all the finishing and paint?

I'm stuck and it's really hard for me to get the body on and off. But I did get a cool gas cap today:) .

Sean