Also I already snorkel a lot, but i do need some gear for SCUBA diving, when is the best time to buy?

The local season makes little difference if you plan on dive trips to warm climates. You can take lessons locally, doing your pool work and classroom work. Then go to Cozumel for your 4 checkout dives.

Many dive shops offer this as a service. This allows you to start and finish your lessons in winter. Also, you can get a better price for lessons off-season.