I can't answer all of your questions, but I can offer opinions on a few...

Every pool I've seen has some footprints and irregularities under the liner. Most of the bottoms are sand and it shifts around over the life of the pool. When I had my liner replaced this year, a basic smoothing job of the sand (in my case sand/concrete mixture that had to be patched due to those irregularities) is included in the quote. Make sure you ask that question when interviewing contractors....

IN most cases, if the liner hasn't pulled too far out of the track, you can use a butter knife and spoon (usually requires 2 people) to stretch it back up and re-seat it in the track. Do this in the heat of the day when the sun will help the liner be more pliable and apt to stretch.

A vinyl liner pool is fine for your area, but be aware that if you ever decide to drain it, that the liner will "float"--so don't completely drain it until you're ready to replace the liner! My pool in Louisiana is liner and I don't have light or main drain either. Don't need it. Don't have any idea how much of a problem it is to add..

If you have no leaks in your liner, and can put up with the cosmetic problems, there is no need to replace it. My new liner installation came with new coping, but again that's something you need to ask the contractor about. Wrinkling is commonly caused by water leaking under the liner, and also commonly caused by letting the pH get too low--if you've got bleaching from pucks in the water, that's probably your problem.

As for when to replace the liner, that's up to you. Obviously you wouldn't want to do it during swim season if it's not necessary. The contractors start getting their new year liner models in about March, so if you go Jan/Feb, often you can get good sale prices on last year's liners. In Louisiana, you can often get a price break if you get it done before Mardi Gras, but I doubt that matters in Alabama.

I also have a Hayward sand filter--sand filters do a pretty good job of fine filtering. A DE filter will filter much finer stuff and "polish" the water better, but they're a PITA to maintain, compared to sand...and you can always throw a handfull of DE into your sand filter to get the DE quality. Cartridge filters are also a PITA when it comes to cleaning-- as far as ease of maintenance, sand filters are really the easiest.

Janet