Connecting between international flights at Miami (MIA) and Fort Lauderdale (FLL)

It would certainly be easier and more comfortable if you were to connect directly in Miami, but an 8.5 hours connection is entirely doable.

Transport options

1. Take the train (http://www.tri-rail.com/airport-connections/). Cost is very low (<5$) but the train schedule is only about once an hour and there are extra shuttle bus rides from the train stations to the actual terminals. I think they are free, but can be hassle, especially of you have lots of luggage
2. Shared Van (https://booking.supershuttle.com/?RezMode=1&direction=RT&_ga=2.154460798.772710600.1526132486-268259906.1526132486 for example). You book in advance and they'll drive you from airport to airport. There may be other passengers and other stops, so it'll typically take longer than a direct connection. Price would start around $45 or so.
3. Better van: same as #2) but you can pay more money for a direct connection and/or have a car to yourself. Around $100.
4. Rental car. Around $60 + insurance. This still requires using the people mover in MIA and a shuttle in FLL, so it's similar to the train. It takes some time to pick and drop off the car. Driving down there during rush hour is NO fun, so I would only consider this only if you are comfortable with heavy urban traffic in the US.
5. Uber/Lyft. $40-$50 unless it's high demand or you have a lot of luggage or people. Very easy, you request when you have your luggage, meet at the pick up point and the driver will drop you off right at your the terminal at FLL. https://www.uber.com/airports/mia/
6. Taxi. Maybe $100? Hard to tell upfront.

Personally, I would do Uber, especially if you are more than one person in your party. Only exception terrible traffic conditions, in which case I would use the train. The good thing about this approach is that you can decide when you get there. Once landed you can check traffic and Uber price & availability. If it's good, get an Uber, if it's horrible head to the train station.