Are your drain lines in for those locations? If it was me, I'd move the sink to the other side of the toilet and next to the door. Just having a sink to wash up is very nice, but there's no need to go through the entire bathoom to get it. It's also nice to have lots of room in front of a shower to change clothes. A bench or seat along that wall would be very handy.
You will need an interior wall for the shower. I'd put the shower manifold on that interior wall too. I don't think it matters wich side you put it on, but I just like to have them on interior walls.
Where will the hot water heater go?
Do you have a place to store towels, soap and toilet paper?
Eddie