I can only answer #1 from my experience. We purchased a top of the line 24' round Swim n Play back in 98. It has stainless bottom rails, stainless bottom plates, stainless skimmer panel, the top rails, uprights and ledge are platic coated steel. We reloacted the pool in 02 to make room for an addition on the house and everthing was pristine except the steel wall, it had a light coating of white powder and very light signs of rust, this is on the inside, outside it was perfect. Fast foward to 2011, I have an area of about 18" square with about a dozen bb sized holes in the wall, this was my fault though. Last year I had a small leak that let water between the liner and wall, I never looked hard enough to figure out where it was. Over the winter the water corroded the steel wall and spring a nice leak which was easy to find.

I dont know how aluminum would have held out in my case, however with my recent repair I think I can get several more years out of the pool. I am inpressed with the stainless bottom rails, they looked great in 02, im my case the steel wall is the weak point and if I had to do it again, I'd probably go steel again.

If you have the space, 33' round is the way to go IMHO. A note about warranty from Swim N Play, if me wall is covered under the 35yr warranty, I would get only 25% off the cost of a pool wall which would still cost me $750. Found the exact pool on Craigslist for $299, I take down, I get the wall and everything else if in decent condition.

Good luck.