Its gona be windy this weekend. Lots of stuff to do off keybiscayne. To the north, fish bear cut, the east the reef and a bunch of wrecks, but your best bet, if it's flats your looking for, is to go south thru stiltsville to the finnger channels.
Normaly more members would have some suggestions, but they are currently very busy planing a chub tournament
When you go out of the channel in Stiltsville you're pretty much over the first reef/patch reef. Just pay attention to your depth finder and you'll pick up on the three reef lines.
As for the flats, the flats near stiltsville can be hard to fish because of the boat traffic. A better bet would be to run further south into the bay near black point. I've heard there's some reds on the grass flats out that way. But honestly, if you're trying to flats fish. It's all about the keys and flamingo.