Hi Butters
I think you have the right idea. Fix the bath to the wall at the position and height you need. The batten beneath will give it extra support. Once ready to tile I would definitely seal the gap between the bath and the wall with silicone - belt and braces job. Don't take it for granted that you can start with a full tile off the bath. Measure the room out - spend plenty of time on this - and see where the best cuts are and which looks the best.
If you are unsure about setting out (sorry if you have done a course or are a
tiler - you don't say) do a search on the site - there are guides galore to setting out a room.
Once tiles are on the wall and cut to the bath (99% certainty), grout ( see guides) use silicone again along bath and corners (see guides on getting a perfect finish) and you are done.
best of luck
frogeye