Where To Start... Where To Start.... :P

Hi Guys! For anyone who hasn't seen my introduction, I'm a retiree on a fixed & very limited income. Bought a tiny 5x8 CT, new, couple of years ago. I chose this one, cuz it was the smallest one I could find with a man door in the side. Anyway, I put in a window, roof vent & some shelves. To date, that's all. Wanna convert 'er, but geeze... where to start...
Okay, I guess FIRST, if it ever stops raining, I'll take some pics & post 'em here for you pic-mongers!
After that, I'm thinkin' rip out the shelves & start from scratch. First question... insulation... some guy told me I should just drill a few small holes in the top of each sheet of plywood, & squirt the walls full of spray-in foam.
Personally, I'm thinkin' I should take down all the ply, insulate with rigid foam board, reinstall the ply, & paint.
Opinions?
Another question, if I do it MY way, how do you hold the foam board in place, while reinstalling the plywood? Thanx!
Okay, I guess FIRST, if it ever stops raining, I'll take some pics & post 'em here for you pic-mongers!

After that, I'm thinkin' rip out the shelves & start from scratch. First question... insulation... some guy told me I should just drill a few small holes in the top of each sheet of plywood, & squirt the walls full of spray-in foam.
Personally, I'm thinkin' I should take down all the ply, insulate with rigid foam board, reinstall the ply, & paint.

Another question, if I do it MY way, how do you hold the foam board in place, while reinstalling the plywood? Thanx!
