Have you ever done this style of texture. I bet not. Have you even done any drywall work at all.

It's how it is done. You take drywall mud, and you mix it with water. Take a mop looking device and put it into the bucket, then put it onto the ceiling. Then pull down.
Another way is to use a sponge. Another way is to use a tile grout float. It was a fairly common texture technique.

You can scrape it some, but it won't all come off nice. You will still have to sand.

It's just drywall mud.

That is what those are. I do construction.
The square box is framed out there won't be any concrete there once he takes off the tape. Find a 2"pvc pipe sticking up. That is where the shower drain will go. The ring on the floor, that is a toilet ring. Not getting away from that one. The way it is currently oriented the toilet can only go one of 2 ways. 90° opposite of the slides. The other two coming up, the #1 is too close to the shower to be the sink, it is also too small. That leaves it the vent. The last one sticking up, that one is far enough away to allow for a vanity. Thus a sink.

This whole area is stubbed out for a bathroom.

1. vent stubout
2. for shower drain.
3. toilet ring
4. sink drain stub out.

When you plumb in your sink, you will need to run its own vent. That will tie into the inwall drain.

If possible, can you move the wiring so it is more out of the way?
For the dirt, you could build a green treated wall to hold it back.

Your switch should be reading 120, coming in when it is off. If it's not, then you have an issue prior to the switch.
Without seeing how your switch box is set up, it would be hard to tell you where and how to proceed right. It depends on where the power is feeding first.
If you can post some pics, that would help too.

You're using one of those small DIY mixers that holds like a few bags max, right? You're doing it backward. Spray the sides to wet.
Add in the bag. Dry mix for about 30 seconds. This helps remove soft clumps. Hard ones, you won't get out. Then spray in water slowly until it is what you want.
Let mix like 2 minutes or so.

Ok. Also, under where the sistered up joists are, put at least 2 if not 3 two X into the wall underneath to act as a post. That will help with the extra weight transfer.

Too many to read through. Yes it can be done. You will have to sister in another joist full length on both sides of the one you want to cut. Maybe even triple it depending on the span.
Next, where your wanting to cut out, you will need to double up both sides. That way your box is strong enough. Will need to also incorporate joist hangers on this too. Now, by moving the projector up those few inches and then literally putting a wall in front of it, is that going to do you any good?

Your HVAC system could be putting that smell in there. Check for that also. It can draw the gases into the ducting and blow it back out.
Had that in one house, one bathroom smelled, off and on. Tried several different things. Even did a smoke test and nothing. Ended up finding a vent pipe going into a cold air return that had a joint wasn't glued by the plumber. Only way I found it was by removing the cold air covering and pulling on the pipes.
Another is possible the toilet seal has failed. Next, look for anything that was added recently. A screw/nail could have went through a pipe.

Not being familiar with what is used where your at, but I am going to bet that the linoleum is going to need to come up along with its subfloor.
New subfloor put down, then new flooring. Another option is new subfloor on top of that now, then new flooring on the new subfloor.
That glue is going to be hard to get up. Almost always it involves nasty Chemicals, heat and lots of being on hands and knees, aching back, putty knives getting glue that won't come off consistently and it needs cleaning.
Just way easier to do the other 2 ways. And faster.