I booked our rental car for September in Tuscany. Want to makesure I did it right.

I assume you know about ZTLs? Here's some detailed info: https://www.italybeyondtheobvious.com/dont-mess-with-ztl-zones

And, of course, you are comfortable with a standard transmission and diesel. Watch your fuel level. Most US credit card will not work in unmanned filling stations so we always use a station with the attended and paid the difference.

Autoeurope for a car from Europcar?
or
Autoeuropa?

It is recommend to rent through only Europcar, Hertz or Avis. Consolidators like Autoeurope use all 3 plus others so make sure if using a consolidator you choose one of those 3 brands.
Also, make sure to visit your local AAA location and get your license translated into an Internal Driver's Permit for Italy for any and all drivers. You don't need to be a AAA member.

I usually stay away from renting vehicles in Europe, but if you absolutely must then I would probably use www.gemut.com - a local USA travel company in Oregon that will work with you personally to get you the vehicle you need at a good price with good customer service. I've only read positive reviews about Gemut and their rental car services.

I agree with the advice to use Gemut.com. They are terrific. Very personalized and if you have any issues, offer a 24x7 customer service. Their free download on driving here is invaluable for a first timer.

Thanks for all the replays . I do have our international drivers permit . I' m looking at the sites that were recommended. I will book our car tomorrow.

I've rented with autoeurope.com and with europcar.com without problems. I always check both sites, sometimes autoeurope has a better price for europcar, sometime directly with europcar is better. You do have to read the fine print to see what extras you may get charged for. When I booked a car in France, it turned out that the much cheaper autoeurope quote would have been much more expensive because of taxes and surcharges.

I rented a car in Milan last month. AutoEurope I pre paid and had insurance through my CC. I was charged 800 euros at the airport for possible damages....A hold on my CC that lasted 4 days. I don't know how to avoid it?

Suzanne, you stated yourself you have insurance through your credit card.
This is a you pay first and then the credit card reimburses you type of coverage which is why there was a hold placed on your funds.
Had you gotten the insurance through the rental company there would not be this hold.

Also, if you are going this route do make sure to check with your credit card that Italy is included. Many that include amny countries still exclude some like Ireland and Italy. Not saying all exclude Italy but some do.
Lastly concerning credit cards some of the fine print is a little scary because they all state in order for your credit card insurance to be valid all other insurances must be declined and the credit card be primary but in Italy it is not possible to decline the required main insurance and your credit card is serving as secondary insurance covering a deductible if you get any coverage at all. Others dismiss this but not sure anyone has ever posted with an actual claim and had a credit card (like Chase) reimburse them with no issues so I think there is some grey area here.

On my trip to Sicily in 2014, Kemwel had a far better price than anyone else, including AutoEurope (they are now under the same umbrella but are different companies) or Gemut. So, check them all, as well as the companies themselves (Hertz, Europecar, Budget, etc).

Be aware that AutoEurope (ending in e) and AutoEuropa (ending in a) are two different companies. AutoEurope generally gets good reviews; AutoEuropa doesn't.