We've made arrangements to pick up our rental car at the 53 via Borgo Ognissanti location used by AutoEurope. It looks like it's just a short walk from the SMN train station. Am I correct in that assumption and, if so, how long does it take to walk there?
Yes, it is only about a 5 minute walk from the train station. You can google map it so that you know exactly where you are going.
You'll want to know where the Florence ZTLs are, go here for a map showing those: https://ztl.comune.fi.it/tzi/index.jsp.......If you accidentally drive into one of the ZTLs, automatic cameras enforced $150 fines and you can rack up several of these in one trip. For more info on that: http://www.ricksteves.com/graffiti/helpline/index.cfm?fuseaction=readtopic&topicID=28422&page=2