Adults only all inclusive Mexico honeymoon

So I don't even know where to begin… we are planning for a late January honeymoon and looking into Mexico! The problem is I know nothing about all the places/beaches in Mexico. I'm not sure what coast is better or pros and cons of each. Here's what is important to us:

• *All inclusive
• *Adults only
• *warm temps (obviously it's Mexico.. but idk if there are certain parts that are warmer in January? we live in the Midwest so we want a warm escape)
• *I'm thinking gulf coast because of pretty water but I also hear the pacific coast has a lot of beauty. Very conflicted here!! Lol
• *good food and variety
• *I am content laying on the beach, my fiancé would love to do things like experiencing culture, or activities such as snorkeling/scuba diving, things in nature. So a mix of both!
• *budget around $5000, number of days TBD

Clearly I know nothing lol. But open on where to start!!