Key Largo is a weekend getaway for me.
I am down there a fair bit.
Things to consider (killing some pre-conceived notions by those that have not been before).
> there are no real beaches there. Plenty of rocky, solid shoreline. Most of it is private. There are parks you can go to to get water access. Most will have an entrance fee for non locals.
> above leads to: very little places to stay with with actual ocean view. If you find one, it's pretty damn expensive. I have found some boutique places with ocean views that are reasonable. im me for info. Rainbow Reef offers lodging and dive packages with close by hotels. I have done that before and stayed at the Mariot next door. Nice hotel with marina view (extra $$). Parking lot view available
> Key West Inn, also next door, is pretty nice,
now. Recent renovations and all rooms have marina (canal) view.
> Doc's diner is across the road from both places and is a must if you like to eat big ass breakfasts
The comments above about crowding on RR boats are true, but not likely during the off season, which is now and the time you are going. I wouldn't fret about that.
Sea Dwellers is a good option as well. Their boat is located across the canal from RR. Their shop is nearby on 1. I have stayed at the Holiday Inn (were their boat is tied up) and would not recommend staying there. They have rooms with canal views and balcony, but they are a joke being so small and your neighbour's window shaker venting right at you. Sea Dwellers run only one boat, but there is plenty of room even when full. I have observed check out dives on both boats, and can say it is definitely more one on one on Sea Dwellers. Sea Dwellers is not known for 5 min surface intervals, RR is (basically dropping you 3 min further down the road on the second dive). I am not trying to disparage RR, I like them as they have their shit together and are pleasant to patronize. But, their boats are run a strict schedule.