Ciao Anne,
Yes, I highly recommend you park away from the center to avoid any risk of entering the ZTL area. You don't have to park way out in the outskirts - you can park closer, but parking will be paid. Free parking has decreased over the years, so just expect in general to pay for the hours you need... having said that, Piazzale Michelangelo offers free parking and is really close to the city. It is also quite crowded, so you might not find a spot right away. You can find specific suggestions as to where to park and then what to take downtown here:
http://www.visitflorence.com/florenc...-florence.html
As for the car return, do you mean you return the car in Florence to then continue on to Venice?
Car rentals are not exempt from fines, but it is the rental agency themselves who have to notify the police that you entered the ZTL area at a certain time to drop off the rental. What company did you rent from? That way I can check the precise address and see what the best way to get there is... normally, if in the Borgo Ognissanti area, then the best is through Porta al Prato (and Via al Prato).
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