you will be able to avoid tolls with a good use of a satnav, but if you want to cruise around the miami area, there are quite a few toll roads, and they're all automated.
So to avoid being caught off guard, check the policy for sunpass for your rental company.
Some like Alamo get you opted in automatically, and if you should enter a toll road inadvertently, you'll only be charged a small fee + the toll itself
Other rental companies will charge you ridiculous admin fees (like $25 per toll)
to be on the safe side, just check.