Going barefoot all the time is not necessarily a good idea especially when you run into a good mix of sand and course coral. Wading booties are good for snorkeling I preferred them over fins (not so much like swimming with clown shoes on).
We rented bikes and liked getting around on them. It wasn't that great the day it rained. But otherwise it was fine. It is bumpy but you learn to adjust when to sit and when not to (you return home with "buns of steel" laugh )
My husband took and wore his tennis shoes and had no problem with sand as it not really fine sand.

Time flys - have fun!