All in all looks like pretty poor work. Almost looks like the drain is above the tile but hard to tell for sure. Not sure what the laws in FL are as far as your recourse, but just tiling over this mess only fixes it long enough for the ink to dry on you accepting the work and voiding your...
The code is 1/4" per foot slope to drain. Its in the TCNA handbook as well. Funny how they point to one section but forget the other existed. Everyone is just trying to get away from your job as cheaply as possible. Not sure what state you are in, but i have to have a license, bond, and...
There is a code for proper slope to drain, sounds like they didn't adhere to that. Should be redone. Yes, you can install new tile over existing tile, but this wouldn't be one of those times.
In the states its 1 year on remodel work for warranty. Tile lasts until the trend changes. I see my clients at the store, or soccer games with my kids. He should be there helping. Never heard of wall or floor adhesives. Makes no sense. I don't have access to your products though, so maybe fine.
Pretty poor contact and trowel technique. Expansion joints at all edges are required. Back buttering helps with bonding, but not required. Heated floors were done properly for years before membranes came out, just looks to be a bad install. Shouldn't be able to see ridges from trowel.
You likely ate the glaze with the acid and now all vapor and everything else under your tile has a quick exit from under your tile. Sealer won't stop it, it's like putting a bandage on the outside of a rubber pool in a very small but real scenario. Pictures would certainly help.
Any change of plane in tile should be Silicon. If your cuts along the tub are really nice and even, color matching Silicon would be fine but if it's less than perfect, white will likley blend it all better.
Sealers usually depend on the type of grout used. Technology has changed grout quite a bit, instead of a 7-8% absorption rate, some grouts claim to be down to 2% or less so don't require sealing. Some people feel you should seal everything despite what the company says. Sealing prevents almost...
Laticrete GTA (glass tile adhesive), and no sheetrock, use wonderboard or another brand of tile backer. The glass manufacturer should have some instructions to follow.
Not sure as to why they are switching, but I have to agree there is less chance of error with sheet membranes. I know plenty of folks who use liquids incorrectly.