Sounds like you both had an amazing time. Switching and exploring new things is a lot of fun.
As for the beads, Making sure to go to the loo before anal play helps alot. But if your going to go deep, douching is probably sensible unless your ok with it getting a bit messy.
At the end of the day, its anal. Kind of goes with the territory. Just remember to put a towel down and make sure to wash your hands etc (especially before doing anything vaginal) and you should be fine.
sounds like you two are going to have alot of fun exploring switching and flipping the power dynamic.
Ps. Im not the one to ask about prostate orgasms, but Here is a good place to look for info