I have used them several times and would use them again. You have heard correctly, it is high season. That means availability is less and discounts are less. The best news I can offer is that January is usually slightly less busy/lower rates than Feb-April.

Not sure what you are looking for in a "crewed" catamaran. Understand that there are crewed boats that come with a captain and cook as a package. Alternatively, you can charter a boat and hire crew (captain + ?) through the charter company.

As a newbie, you may want to try a broker.