As a sailor in Miami
I can tell you itís expensive. Dinner key is friendly to live aboard but you can only get a mooring as the dock
waitlist is years long. South Beach Marina would be able to get you in within a few weeks I bet and are friendly to live aboard but the prices are astronomical ($1,800-$2,000/mo for your boat if they insist on the minimum length charge they quoted me). You can try the Pelican Harbor Marina, short wait list for a ďtransientĒ slip that you can just stay at indefinitely (I know others who did this there). Technically they donít allow liveaboards but itís more of a dont ask dont tell policy. Transient slip would run you $600-$700/mo and is very well protected (even in a hurricane).
Miami Yacht club is nice but theyíre very hard to get a hold of as I could never get a call back from them about a slip; great restaurant though.
Feel free to PM me if you want to chat.