Since we are siting is Bimini waiting for a window to cross to Nassau, here is a late response to your question. It's going to be cold coming down the ICW in February, but you know that. Weather in Keys will be nice, but fronts will still be moving through. The Dry Tortugas is more of an open roadstead than a sheltered anchorage and can get rolly and rough in strong winds. It is 80 plus miles back to Key West, and more to the Florida West Coast, so it is possible to get stuck in the Dry Tortugas waiting for an opportunity to leave. If you wait until late March/April, the fronts quit coming south and the weather greatly improves. The Floridians all cruise in May/June, thinking only the crazy northerners mess about in the winter winds and cold. Have a good trip.
Roger and Anne