Installing a drop in tub

Probably won't be doing this til the spring, but been thinking about it a bit (my buddy is putting a tub in at his rental) and just want to know what I'm going to be up against.

This is how the bathroom sits now (minus the tub, pulled it out when we first moved in):




Drain and supply is on the right side of picture. Bathroom is on second floor but no access to plumbing from finished basement.

I plan on installing a drop-in tub, preferably flipped around so person would be facing to the left (out the window). Going to outline how I'm thinking it goes and any questions (bolded) below, please chime in since I don't have much of an idea how it's supposed to go....

- pull off old surround and carpet (yes, there's pink carpet on the walls....)
- pull up old linoleum
- cut off existing drywall, at least to where it's going to meet the deck of the new tub, probably higher and replace with greenboard or ..?
- build frame to place tub into. 3/4" plywood for decking on top of 2x4's
- cut out floor (joists run left to right) and run drain and water lines to left side.
- set tub (on mortar bed from what I've seen on youtube)
- hook up drain and faucet
- test for leaks
- sheet sides of frame with greenboard or cement board?
- tile sides, deck and floor

- how do I know exactly where to put the drain? Do I build frame, place tub in and mark it then?
- does the p-trap need to go right after the drain or is it close enough I can run the line to the existing p-trap.
- do I need to tile on top of the deck before placing the tub or do I tile up the edge after it's set?
- if I have to replace the wall with greenboard/cement board, how high above the tub rim do I need to go if at all?


I probably missed some pretty big steps.... please fill in the blanks for me!

Thanks!

Is this the tub or are going for new?

Going for new, something like this:



The pic I originally posted probably confused things, sorry about that (only one I had handy).

What usually happens is, you get the tub on site and then locate the drain. I think the plumbers will want you to put the trap right at the drain and maybe they will question distance to vent. You want to keep the water lines away from the outside wall. If you tile the deck first you have to find a way to stop the tub from sliding around and morter bed is requemended but seldom happens.
If you center the tub right and left make the back of the deck the same as the sides. Build the front wall out of 2x6 so you have a nice size tile there. Cover the deck front and top with cement board and if you are tiling some of the wall say 16" do 14" of cement board and the green board above that. Solid blocking between the studs is required just above the deck hight and at the join between the cement board and the green board. It's bad enough when some falls in the tub" it's worse when the elbow goes thru the wall.