Can I rely on buying tickets from the gate or should I get them beforehand?
I believe if you get tickets from the gate there's either less, or no, fees. But Tampa/Panthers is gonna be a fairly busy game especially on a Saturday night so selection might not be great. I've also seen lengthy lines outside the box office on some games. I'd keep an eye on stub hub and Ticketmaster leading up to the game, and people often sell tickets on the Facebook group.
How's the parking? I do have a car but if it's tricky I prefer public transportation. Then I could grab few beers too.
Do not rely on public transportation, especially if coming all the way from Miami. It sucks. Parking at BB&T is a breeze, if you buy a single game ticket there's a small surcharge on it already that covers parking cost, if you buy from a second market it probably won't have that attached (or if you're going to buy from the gate0 then it's $20 as you go in. Lots of people park at the mall opposite, and walk over.
Any recommendations on restaurants in Miami? I really like seafood.
I don't spend much time in Miami so I can't be much help on that, but the seafood restaurants in Fort Lauderdale are generally pretty good for the most part so I'm sure you'll find something good without too much effort down there. If you head to Fort Lauderdale, then 15th St Fisheries is good, Kelley's Landing seemed decent and Southport Raw Bar always comes up too. Look along the water and you'll find lots of choice for all the cities here.