Awesome!
SunLife Stadium is very well put together with signage and the sort. As someone already said, near Gate H. It will be a booth right outside of the stadium, facing the stadium as opposed to being attached. You'll either follow the signs or see it pretty easily if you're around the right gate.
To be honest, taxis and public transportation aren't Miami's thing (or Florida's, for that matter). They'll likely be there, but you might have to call one in. And it will likely be a little more expensive than you expected, although that really depends upon how far your hotel is from SunLife.
Finding a hotel would be another thing. SunLife is NOT in Miami. It's in Opa Locka/Miami Gardens. Miami is still a good 30 minutes southeast from SunLife, and Ft. Lauderdale is a good 30 minutes northeast. There are hotels around the stadium though. There's hotels just about everywhere, really.
Again, there is no public transportation in Florida, unless you're actually in the city of Miami, Ft. Lauderdale, or West Palm Beach. And even then, it's pretty weak. Depending upon how long you're staying, you might be better off renting a car. Everything in South Florida, and Florida in general, is very spaced out. Taxis, when present, are very expensive.