I think your schedule is too busy

I have done the similar route last year: Orlando->key west->Miami.It took me 7 nights. There are lots of water activities in Key West: parasail, water jet etc.However,things are not cheap there. Don't forget to sample the famous key lime pie. I really enjoyed the driving part.Everglade is a must.So is the famous south beach in Miami.Tempa is a nice place and relatively cheap.Clearwater has wonderful beach and the grouper sandwich there is the best. There are so many things to do there. I am sure when you come back from the trip, you would want to go there again next year.
Note: Florida sunshine is very strong even in winter.