Hopefully someone with direct experience will check in. My sister-in-law lived in Key Largo for a decade and with a very shallow draft power boat was all over the place. When visiting, we went out along the route you're talking. I recall shallow, shallow, shallow unless in a channel and the need for local knowledge. I've just emailed her to ask your question. Will post when I get a response.
Quick reply from Sis:
There is a Bay-side (what you call inside) channel which is well marked on the charts. Follow the charts and you will be fine--it is deep water in the channel and no mast issues. However, it meanders around and isn't direct--so you need those charts! Paper charts aboard are better, IMHO, however, if you don't have the correct ones, you can download charts for free from NOAA website.