Replacing these parts yourself is not hard at all. There are many write ups about R&R the rear bumper. The same goes for the position sensor. I would also wait to see what the compression styrofoam looks like before doing anything. Actually the foam sold at Home Depot or Lowe's can be used to fill in any compressed styrofoam.
All in all the best plan is to take the old bumper into the paint shop with the new bumper and have them match the paint and also paint your position sensor at the same time. As long as you can drive something else for a few days you should be good to go.