Welcome to the forum, Dennie.
First, there are plenty of areas where the codes says a shower needs to be a dead minimum of 900 sq/in of floor space, with no less than a 30" measurement in either direction. That's the first thing you might wanna consider.
You can buy a kerdi tray and chop it on 3, perhaps all four sides to squeeze it into your opening. But realize the tray may hinder your installation if it doesn't reach your drain location. If you wanna keep your options open, consider mudding the floor instead.
The drain pipe needs to be 2" from the drain in the shower floor all the way out the house. Nowhere can it be reduced or be constricted with anything less than a 2" drain. So if you have a 1 1/2" drain pipe now, you're likely going to need to replace a run from your tub over to where the drain meets up with a larger section of drain pipe. So this isn't always an easy thing to do under a slab. If you can figure out where your drain goes and meets up with other parts, you can get a better grip on how much concrete you'll need to bust open. Your floor is likely to be 3"-4" thick.
Yes, you can build a wall out of glass block if that's what you mean. Just make sure the configuration of whatever sliding or swinging shower door is sufficiently supported...you can't hang a door from a wobbly wall.
As for tile, go to a real tile store instead of a big box store for starters. It's hard to say this tile is good or that tile is bad. Rather, it's more important to choose tile that's appropriate for a shower. For example, a polished marble would be a poor choice for a shower due to the maintenance issues associated with it. A porcelain tile would be a better choice due to it's toughness and low absorptive quality. Another thing you need is consistent tile in terms of it's overall dimension...or caliber. Sometimes the big box stores have the same tile for less than a tile store and may be due in part to it's inconsistent size tile from piece to piece (not very tight tolerances on caliber). Inconsistent tiles are more difficult to install and may detract from straight groutlines.