If your snorkle equipment doesn't fit well it will leak and your experience will not be as nice. I suggest you buy from somewhere that you can try on the mask first or return it after buying if it doesn't fit when you get home. To check the fit press the mask up to your face without the strap going behind your head and breathe in through your nose. If it stays in place without the strap you have a good fit. Not all shapes fit all faces. Try to buy a snorkle that will "purge" through a valve at the bottom of the snorkle. This will keep you from having a big mouth full of salt water if you get it in your snorkle.
As to you question about the disinfectant wipes, I (and this is just my personal opinion) wouldn't want the chemicals in my mouth and I don't think that they could get into the tiny breaks or tears in the rubber or silicone of the mouthpiece to truly sanitize. Bleach is the best disinfectant and if I HAD to use rental gear, I would pack a small travel bottle with bleach that I could sanitize with, but then again you are probably going to get no choice about the size and shape of mask so you are taking a risk of leaks and the snorkles that are used for rentals are non purging snorkles in most cases.
Unless you plan on diving down alot to see the reefs and fish up close the fins provided on tours or rentals will be ok, but an experienced snorkler or diver will definately notice the difference between the plastic fins and a good quality pair of fins. You will get better preformance from quality gear and if cared for properly it will last for many years.
