I'm a newbie, waiting on my tub, but I've read a LOT of posts, so I'll try to answer some of your questions with some semblance of knowledge.....
Chemicals are something you don't want to "guess" at. If you bought your tub from a dealer, ask them if you can bring in a sample of your water to be tested, then ask them for a basic rundown on what chemicals you'll need to bring the pH, alkalinity, etc into line....
Many people on this forum use bromine successfully, and others swear by chlorine. Those are the "big two" sanitizer systems, supplemented by mineral sticks and ozone (the big two supplements to keep water sparkling clean).
The patio may not be an issue, depending what the manufacturer requires. The only one I'm familiar with so far that specifically states NO SHIMMING allowed and requiresb a concrete pad or suitably reinforced decking is the largest of the Hot Spring tubs. Check your owners manual or call the dealer to be sure that your tub manufacturer doesn't require something specific like that.
Regarding tilt: from what I understand is that if the tub sits an inch or so crooked through the entire length of the tub (no bulges in the lay of the brick), it should be fine, just may be annoying visually to you. Just be sure that the filter area is at the deeper end...
I'm sure others will chime in to correct me where I may be off base, or to give other pearls of wisdom.....but in any case, enjoy your new purchase! (I know nothing about Gulf Coast tubs, sorry)