I just went to Metro last year, and for your questions, I got to say that you SHOULD prepare for what your friends said since Florida is really hot during Summer. Though, lately it has been raining a lot more which means Mosquitoes! Yay (not yay ;3
. But can't say what will happen if you're going next year so can't tell if it'll rain. A few things you should know about the con, I believe it has three floors for the con specifically. 1st has registration, food, dealers room, many of the panel rooms, and the floor near where the Fire show is. And I'll get back with the fire show in a second. 2nd floor, is Artist Alley, and 3rd is where the big events are held that you need to go in line I think 2-3 hours ahead of time.
Events that you should go to are the Masquerade and fire show. The fire show is an event the con has every year with a nice display using fire done by professionals who can handle the tricks they do. And lastly from what I can tell about the location, I can't tell you much as I didn't wander too far but the area is very beautiful and nice for photoshoots or just relaxing in. Even witnessed a shoot where this superman cosplayer went up the steps near us and did a shoot there, with their cape flying in the wind behind them.
I do suggest going to the Metro-con facebook page if you can as that place always gets answers and people are really friendly in it as long as you're not purposely saying bad things to them that anger the admins. Also, I wish you the best for when you actually go here as Florida has wonderful conventions! Though you should take a week off if you have work and just be here for a week or two or experience the convention and the theme parks here!