Congrats, I will be going down to Miami also. It was my #1 choice and a longshot but I got in. Let me know about your visit... the apartment hunt especially. I'd really like to live at South Beach but I hear mixed things. Let me know what the apartment situation looks like around Coral Gables. Good luck.
I would talk to the admissions office, even if just briefly, about the apt situation. They can point you in the right direction. Also I've heard that they send out information on housing/roommates in March (it said in my acceptance letter) and I've talked to a few students (when I was down there) who said that would be a fine way to find an apt.
I stayed in Miami Beach while I was in Miami and it was amazing. South Beach might be a bit sketchy at night, but I think it would be an okay place to live -- but not necessarily if you're in your first year of law school I think. You really don't realize how far South Beach is from Coral Gables if you're just looking at a map, but it's actually like 12 or 13 miles. That doesn't seem like a lot, but I wouldn't really want to make that commute every day. If I were you I would live within walking/biking distance or somewhere on the elevated train line. U of Miami seems to not have much parking (I certainly wouldn't want to deal w/ it everyday). Plus, when I was there I took public transportation from South Beach to the University of Miami one day. It is a bus ride all the way downtown and then a transfer to the elevated train. There is no easy way, in other words, to get from south beach to coral gables by public transporation.
I wouldn't panic too much about housing -- if you went to college in a place similar to where I did (ann arbor, mi), you might be used to signing leases in November for the following year... I think that's highly unusual in the real world. Especially private landlords (often the cheapest and best housing) probably list properties in most cities starting in January or so if it is largly student housing. But then I guess many landlords don't necessarily run by the "academic" calander anyhow.
Well, okay, the point is that people at the Univ of Miami can tell you where the students, esp. the law students usually live. They told me when I was there that some live within biking/walking distance of campus, others on the edge of miami on the train line, etc... but I forgot part of what they said. BTW another thing about South Beach is it is supposed to be one of the more expensive places in the whole area to live -- so another reason why it might not be the best place to get an apt. And besides, you might not be doing much laying on the beach your first year of ls anyhow.