I will be installing the drain pipes for my new basement floor, I know my layout and I've done a complete bathroom before, just not a basement bath. My questions are about breaking the concrete up.

(1) Use a saw, jack hammer, or sledge? From the reading up on this I've done:

-i'm concerned about the precision of this so I don't take out more than needed, and cracking close to the external wall. This makes we want to go with a wet saw so I can do long clean cuts, but I've heard the dust and spray is unmanageable

Jackhammer or sledge.
-the replacement concrete holds better on a rough edge versus a smooth edge. This makes we want to go with jack hammer.

I've also heard of a guy that just went and bought a some masonry blades for his circular saw and cut the slab halfway, and finished it with a sledge. Cheaper

(2) In cutting the trenches, I was planning on making them about 10" wide and 12-18" deep. When the plumbing is in there backfill it with #57 put a vapor barrier down with some overlap if possible and pour the concrete. Is this normal procedure??