Is there parking for my rental car available at the Florence Rail Station?
Yes, but you need to be extremely careful about getting there so that you avoid the dreaded restricted zone with 100E fines.
Parking your car there is not recommended, because doing that makes it likely that you will accidentally stray into one of the ZTL zones and that can cost you hundreds of dollars in fines.
this article explains everything & has maps
Locals and other regular users of the train station have their license plates registered in the city computer, so they don't get fined when their license plates show up on the city's many automatic cameras that enforce the ZTL regulations. That's why they're able to park there.
Technically, there's a way to do it without violating the ZTL's, but people here have tried, taken one wrong turn, and gotten the big fines in the mail months later. Not worth the hassle or worry.
The easy way: look at the maps in the link, and park somewhere well outside those 5 zones and take buses or taxis into the historic center.