There's a good chance your trip will take longer than 20 minutes to get there with traffic - especially if you're travelling up 4. We stayed offsite recently and was only like 5 minutes from the front gate, but it still took us an hour to get to the Magic Kingdom, 20 minutes for the other parks. Magic Kingdom takes so much longer cause once you park you have to walk a long ways (even if you park close) and then take the monorail.
I'd take a mid day break but leave property and go to a nice air conditioned restaurant for it, not all the way back to your place. You really need to be at rope drop to get the most out of your ticket. It's less crowded then and you can do so much more. If you can make rope drop, you can save all your fast pass selections for the afternoon, after your mid day break. Make sure you plan your fast passes wisely!.
As far as the heat, the good thing about Disney is there are plenty of places to cool off. Several in door attractions and gift shops. We also got endure towels before we went. You can get them wet at any fountain, snap them, and hang them around your neck. They work great. To me AK seems the hottest place. They don't seem to have as many places to cool down as the rest. At AK go to Planet Watch during the hottest part of the day - that seems the coolest. or plan to watch Nemo or the Lion King. Both of those shows are in air condition - and must see shows too by the way.
As far as itinerary - I'd suggest going to all 4 parks since you have park hoppers. You can go to a different park after your mid day break. I'd suggest MK, AK, and HS for your 3 evenings. You gotta go to Epcot though so do that one morning for rope drop so you can ride Soaring. Do your girls love Frozen? If so they'll have the new ride in Norway for Frozen. Be at the World Showcase for rope drop (World Showcase opens an hour after Epcot opens so you'll have time to get Soaring in first) and hit the new ride and meet Anna and Elsa. There's other princesses around the showcase to meet as well and their lines seem shorter than the Magic Kingdom. I'd suggest going to the parks all day on M, W, and F then the water parks on Tues and Thurs. (IF your Tampa day is relaxing do that in the middle) The water parks aren't an all day event so you can perhaps take it easier on those 2 days. You actually could go to BB in the morning one of those days and TL after a mid day break. That day would wear you out though.
Happy planning! Planning is almost as fun as going for me.
