In #1 you really need to consider headering, support for the header, milling the studs to conform to lath deformation caused by tile masonry base coat.

2) "I have a situation" To quote Dave Hester YUUUP

"Both doors would need to slide to the same side and could either be enclosed in a pocket or left visible."

If you are building a pocket in the room, why do you need two doors?

If the pocket is in another room or outside the building envelope, how is it going to be encased or wether protected?

In #2, an 82" wide door is a lot harder to come by than 2 42" doors. In open position, the doors would park parallel to an existing wall. I may or may not build a pocket to enclose them. I'm more interested in experiences using bypass doors in a floor to ceiling application that require both doors to slide out of the door opening.

I have pocket doors into existing walls by only removing the finished wall on one side.

It helps a LOT if it is NOT weight bearing wall.

I typically use 2x6s on the flat as studs on each side (sometimes milled down to 1.25 in thick) and then steal a little floor space on the removed wall side forthe3adidtinal wall thickness.

You can just fit a 4x4 1.25 inch deep electric box with a plaster ring into either wall (watch out for screws on the back of the box).

Where your difficulty will arise is in finding the hdw. which allows a square door make a square corner, and still have it meet the wall completing the "divider". The second door necessarily needs to be on a traverse track.

Were I you, I would sincerely investigate accordion doors and the possibility of recessing into a wall cavity.