Hi. I'm another person who used to live in Miami, but not for grad school, so I don't really know the situation on where to get housing. My one piece of advice is this:
You NEED a car. With air conditioning. Public transportation in Miami is a joke, and it's far far far too hot for half the year, so walking is very difficult. Miami was also built in an era of cars, thus things are very spread out. Unless you are a super hard-core cyclist, there's no way of doing Miami without an automobile.
Ok two pieces of advice - Sun Juice Smoothies in South Miami is quite close to campus and delicious - kind of like Jamba Juice but much better. It's also the kind of thing that makes you feel good about going to school in an (almost) tropical paradise. Seriously, while working out the expenses is probably not fun, once you get there Miami is a really fun place to live.