Most manufacturers offer their spas without the skirting.You can install either a skirted or unskirted tub in-ground. You can dig a hole and build a box (concrete or cinder block) that the tub will sit in with one side 3' wider for access to the equipment(if your tub is 6'X6' the inside dimension of the box should be 6' X 9'). Build the box so the top of the walls are just below finished grade, depending on your finishing materials. The elevation of the floor should allow the tub to sit on the floor with the lip slightly above the finished height of the walls (not hanging from the walls). Set the tub in place and landscape up to it. Build a removable wooden "deck" over the equipment area. Don't forget to bring power/water to the equipment area. This will only work provided drainage from the bottom of the box is not an issue.I have left the bottom of these boxes gravel.

Installation failure, likely the grout was mixed too wet, or was washed too soon after applying. It could be a waterproofing issue too. Do you have pictures of him installing it? Your installer needs to come and look at it.

Here is a link to google, how that backsplash should have been installed. There are some u tube videos too. I watched one video, where they used grout, between the countertop and the backsplash, and grout should not be used there. Caulking shud be done between backsplash and countertop. My backsplash is also caulked in all the corners, rather than grouted. Once you watch these videos and read these articles, you will see that your thinset was put on improperly, and thats why your tiles are falling off. Please read carefully. https://www.google.com/search?source=hp&ei=uI4VW7HdLszKjwTtrqSoAw&q=how+to+install+glass+subway+tile+backsplash&oq=How+to+install+glass+subway+tile+&gs_l=psy-ab.1.0.0l3j0i22i30k1l3.3755.12143.0.14244.41.29.3.9.9.0.173.3348.9j20.29.0....0...1c.1.64.psy-ab..0.41.3556...0i131k1j33i22i29i30k1.0.70wb9L5GlO8

FWIW, I live in a high rise condo in Los Angeles and recently finished a gut remodel which included taking the shower to the studs and some reframing of walls. The Code in Los Angeles for a multi-family high rise requires steel framing and studs so there isn’t any wood. The framing in the shower and everywhere is metal. I imagine Code for a high rise in any jurisdiction also requires steel. I got a bit of education in construction as I also learned that the metal framing has to be placed at specified spacing. I would imagine this is for fire safety as well as structural integrity but a structural engineer would no doubt have the exact reason. Just another reason why hiring a designer and/or general contractor familiar with high rises specifically is a good idea to minimize screwups.