Bathroom tile repair
Don't waste your time trying to keep damage to a minimum. You are gonna have to patch the wall anyway. If you are installing new pieces of pipe, you will need plenty of working space, so cut  a large hole (as oppossed to many little holes); You or the plumber are gonna end up doing that anyway. And patching a hole , say 8" x8" takes practically the same time as patching one twice that size.
Cut you drywall along the edges of two studs, then nail 2 sections of 2x4s to each stud, in order to have a way to attach your new piece of drywall for the patch. Use drywall screws, not nails. 
Unless you  are planning on using the existing tiles, just remove them with a moulding pry bar and a hammer. No matter how careful you are, Murphy's law says you will break a tile or 2 while trying to remove them in one piece.
Are you sure there is sheetrock behind the tile, and not a substrate made of mortar and metallic mesh?