Rental pick up in Florence: I picked up on a Sunday at the Borgo Ognissanti location in Florence. Easy enough and getting out of town would have been fine if I had just used an old fashioned map (see below). But it was fine. But. A few days after I got home, there was a charge from Europcar for about $42. I contacted them, and they got back to me saying that this location is normally closed on Sundays and opens only by appointment or arrangement and that's when this charge applies. But they said since I wasn't made aware of this, they said they'd refund the charge. It hasn't been done yet, but it hasn't been a week yet. I did the rental through Autoeurope that didn't say anything (that I remember) about Sunday rentals being an extra charge. So be aware if you're picking up on a Sunday at any locations other than the main outlets that may want to change you extra. Good on Europcar though for taking care of this (assuming they really do).
Car rental returns at FCO: I returned a rental here a few days before spending time in Rome and it's not bad at all. Just follow the signs to Car Rental Return. Signs are also in English, so it's easy. And quick (ish). They did a quick look over and declared it damage free (dirty, but no new dings), and that's it. Then train into Rome.
Validating at FCO: Validate as soon as you go through the turnstile to the trains. You don't want to walk to the end of the train for a seat and then remember you have to do this, because the only validation boxes I saw were near the entry.
Back to the GPS: I had google maps and waze on the phone and planned on using those, and hoping the car would have bluetooth. It did, but wouldn't recognize my phone. (Stick shift I'm fine with, but this new fangled technology, nope. Maybe I'm much older than I think?) Anyway, when I plugged the phone in to charge, it would automatically play the music on my phone, which was set to Rick Steves walking tours. I kinda hated his voice after messing with this a few times. Not Rick's fault (probably), but it was frustrating. Didn't want to let the battery die completely, so ended up pulling over more than I wanted to to check the map. I decided that the better way to do this (also because neither google nor waze pronounces Italian very well), is to note the towns you'll be going through and follow the signs to those towns. SO much easier. Especially when I got down to southern Tuscany (Pitigliano/Saturnia area), which is pretty well signed. Non-Luddites can ignore all this.
Edited to add that Google maps does work really well for figuring out the local bus lines in Rome.
Watch for the signs that say start with controllo elettronico veloce something something. I was on this site to make sure I wouldn't get caught by the cameras, and paid attention on the highways, no problem. But the signs still didn't connect with my brain for a couple of the smaller towns and 30kph is really slow. They make it easy and obvious and I was still dumb.
It's all worth it though! Now to sit back with a glass of Italian wine and see if the speeding tickets come.