We were just there a few weeks ago. If you can get a mooring at Coconut Grove Sailing Club do that. It’s easy and they are wonderful.
The public docks are open and are in great shape. I’d lock up your dinghy there and most places in Miami
, just like I would lock a car.
An alternative is to go across the Bay to No Name Harbor and meet your guest there. You can tie to the wall during the day with your boat beginning 8am until 11pm. No overnight allowed on the wall.
You can also anchor inside or Outside No Name Harbor and dinghy in. They’ll probably be 25-75 boats there, many getting ready to cross to the Bahamas
There’s a restaurant and a bar in No Name Harbor. And download the Freebee app and you can get free rides around key Biscayne where there are multiple restaurants.