I'm with the others on the tile layout. If the tub is a whirlpool one with a removable side, then you may or may not want to tile a couple inches(give or take) under the side depending upon how you want it to look.
You have to have the plumbing line up. Chances are you can replace the trap with a new one and rotate it the 3/4" to line up. Not easy working in a tight spot but that's why plumbers get the big bucks. It also depends upon what type of pipe you are dealing with and if this is on a basement slab or upstairs. Dry fit your tub and plumbing before fastening everything down.