+ The reason for the big filter is filtration. I won't ask you to hunt for them, but there are dozens of threads here from AG pool owners who find that their pool is still cloudy weeks after they've killed all the algae. I can pretty much guarantee that, when your chemistry is right, your pool will be the just about the clearest AG pool you've seen. Pools with DE filters may be a bit clearer, but they are a nightmare to work with when there's algae or another problem.

+ As you can see by following the link, 1.5" PVC pipe at Lowes is about $0.60/ft

+ 1.5" ball valves will probably more like $10 each, depending on whether you get them with a union or not.

+ I'm not sure why you have to do the installation; it shouldn't be harder to install this equpment, then the original combo.

+ For a pad, if you want to save a bit, you can get the 12" x 12" x 2" pavers and use those, instead. You'll need to put a bit of effort into leveling the ground underneath them. I'd get 12 pavers, and double stack them, so you're 4" off the ground.

+ If you're doing the piping yourself, use this pipe dope. It's much easier to use than teflon tape and gives a better seal. You might find it at your Lowes, but it wasn't listed online, so the link is to Amazon.
Rectorseal 31631 1/4 Pint Brush Top Tru-Blu Pipe Thread Sealant
+ While you are on Amazon, you may want to get this strap wrench set; a lot of people damage their pipe fittings using a conventional pipe wrench or channel locks.

+ Also this Oatey 'blue glue' is more forgiving than some and works well. If you've never fitted PVC pipe before, READ instructions before you start.

Hope this helps, rather than overwhelms!