Renting a car for our upcoming Italy trip and we have questions about fueling up.

Are you talking about unmanned stations at night or Sunday?
You pay at the pump before fueling. Insert euro bills at the pump then fuel.
Pumps accept also pin & chip credit cards.
During the day stations are manned and have both full service (servito) or self service ( fai da te=DIY). Often even when I choose the self service the attendant still comes and fuels for me. When the attendant fuels for me I always ask for 'il pieno" (fill it up). When you are done give him the money. If you use a self service pump you insert the money (or the credit card) at the pump. You can probably pay the cashier first if you want. I doubt the self service pump lets you get gas and pay later. Too many Neapolitans would be driving away with a full tank without paying.
I don't think you should worry about these details before going. It's not that different from the way you refuel at home except for the fact that at night there is nobody at the station and it's truly self service (but the pumps accept bills)

Most will probably be Autogrilles out on the Autostrada during the day. Thank you for the info. We leave in just two weeks and we are down to little details such as this. I was just curious as last time we were on a tour bus.

During the day there will be plenty of attendants who will help you figure out how to fuel and how to pay. Besides the difference in price between full service and self service is just 3 to 6 cents per liter in Italy therefore if you feel uncomfortable pumping your own gas or paying at the machine you can always go to the full service (servito) line. On an average full tank of 40 liters (over 10 gallons) at today's prices of about €1.43 per liter of diesel (most cars are diesel) the difference is between paying €57 or €55 for a full tank. Not a big deal. You might as well use the attendant. that way you save yourself the nasty smell of the diesel fuel in your hands.

Use the paper towels to handle the pump, or carry some wipes to get the diesel off your hands. It's so much grimier than gasoline and often all over the pumps even when they look clean.

Thank you very much for all the tips! It's much appreciated.

Plastic gloves available on or next to diesel pumps at most filing stations are much better to prevent diesel on the skin rather than wiping it off afterwards.

Be sure you know which fuel you want and what colour hose and filler that is. They may not be the colours you expect.

At many pumps you will be offered a premium diesel and a cheaper one. The premium one might be touted as extra clean or with some additive. For your purpose, the cheap one is all you need.

The best prices in many areas are at service stations associated with large hypermarkets such as Carrefour, although there are not many of them. These are restricted access - you drive in, pump the fuel and pay when you exit at a cashier either cash or credit.

kathy a word of warning, be 100% sure which fuel your car uses (diesel-regular) and be 100% sure what fuel you are pumping. I learned this the hard way as the names of diesel and gasoline and the colors of the pump handles change when you go from one country to the other. I know it sounds silly and it was a stupid jetlag fueled error but just be sure. It made for a good story later, as the Italian tow truck guy, the mechanic, and their families were truly unique and did not rip us off, and we spent some time in small town Italy that we would otherwise have missed but it was a $400 mistake..so be aware as you pump lol.

Try viewing the image url below: left to right. Super Blue with the white handle is premium gasoline. Senza PB with a green handle is ordinary unleaded gasoline. Diesel Plus with a yellow handle is premium diesel. GasOlio with the blue handle is ordinary diesel.
http://www.tp24.it/immagini_articoli/19-01-2015/1421647061-0-continua-a-scendere-il-prezzo-di-benzina-e-diesel-a-trapani-e-marsala-ecco-dove-conviene.jpg

Are petrol stations in abundance or should we be careful not to let our gas tank get too low? We will only be traveling around the countryside of Tuscany. Pam

I'm in Tuscany now. The stations are numerous and all over the area. Not a problem finding one.