If your vision is anything short of 20/20 you may benefit enormously from prescription lenses. But these need to be ordered 1-2 months ahead of time, for your own suitable mask.

This only applies to people with short sight (near vision). No prescription lens will help you if you're long sighted, though for diving when you need to read instruments there are magnifying inserts you can get.

We (Protech) have some masks with generic prescription lenses that aren't ideal but certainly can help. I believe some others also have some, but I don't know who.

Fins are indeed easy to rent, unless you have very (unusually) small or large feet.

Correct use of a snorkel isn't obvious and some training is useful. Really experienced snorkelers often prefer a simple bent tube to the more elaborate self-draining or "dry" snorkels.