Plumbing Questions? Ask a Plumbing Expert.
Ill answer as best I can. Cutting the slab, id use a walk behind saw with a diamond blade wet, to keep the dust down. 24" wide so you have room to work with.
Rough in for a tub depends on what you are buying. Steel tub with porcelain enamel is usually 30" wide. The tubs we used, during the building boom, roughed in at 14" off the side wall and 1" of the drain side wall. Thats to the center of the drain pipe leading to the tub.
Toilet well that should be roughed 12" off the back wall (finished wall measurement" to the center of the pipe and a minimum of 15" from the center of the pipe the the left AND the right to the edge of the adjacent fixture, ie 15" to the edge of the tub and 15" to the edge of the vanity (total of 30" minimum)
Lav/Sink, center the stack/vent and the drain should be 18" center from the floor
Id take the water lines overhead.
In all honesty, Plumbing codes vary sometimes radically from state to state. Any diagram I draw im almost sure would not be up to your ares codes.
If i was in your shoes, id call a local plumber and see if he'd work with you and maybe you could do the cutting and digging, closing the slab, installing the sink and toilet, stuff like that. i don't know your level of experience, but this inst all that simple a job