Welcome to the site, lots of great info here. Im from Tucson originally, live up in Mesa now.
You have a solid base here, lots of potential. If you change your mind on going power window, I have working crank set ups for both doors for sale.
As for the gas filler flap, I'd suggest looking for a third gen Camaro at the junk yard. Those license plate holders/flaps are made to stay down when dropped instead of slamming up, its a nice little upgrade for minimal work involved it just needs a little spacing to the mounting holes.
When I went from crank to power windows I just used the crank window door panels and put the switch in the whole that was already there. The mounting tabs/bracket for the switch hold it to the door nicely and the switch bezel itself covers the hole so there is no noticeable gaps.
As other have said, welcome and ask your questions as they come. Lots of good knowledge and help here. And we love photos, post as much as you wish.