You may want to ping "CruisersForum" which has a couple folks based in Yucatan s d Belize area.
My knowledge is land based having spent quite a bit of time in the Yucatan. My understanding is Isla Mujeres is a decent liveaboard marina for cruisers. Puerto Adventuras near Playa del Carmen is sort of like Marina del Rey with many different options. It's probably fairly expensive but a comfortable place to live. Southward, not much at least in Mexico. I know nothing about Belize.