I am planning a similar trip but no dates yet.
I am going to head for "West End" at closest tip of Grand Bahama Island. It is 54 mls from Riviera Beach Fla.
When it's calm as it normally is the first couple hrs of the mornings here, it would be a no drama, great trip.
If it's blowing like it was last weekend (20-30 winds w/6' waves) you wouldn't go. Key is, if you launch in good water/weather, in a fast boat, you're in.
Scariest part is crossing the Gulf Stream 1/2 way over. If you lose power while in it, you will be heading for New York @ 3 - 5 mphs and quite possibly out or radio range to shore/help.
Bimini Island is even closer to Miami at I think 44 mls.