Tolls on the drive from Venice to Tuscany to Sorrento

Toll booths have a variety of options, just pick the right line - signage is overhead. Lighting will only be a problem on smaller roads, probably near your agriturismo, but not on main roads.

In American toll highways and turnpikes you generally have toll booths every a certain number of miles and at each toll booth you must deposit some money or pay remotely through a transponder.
In Italy toll booths are only at the freeway entrance/exit ramp. When you enter a freeway you pick up the ticket from the booth machine then when you exit the freeway you give the ticket and pay at the exit booth based on which entrance you picked up the ticket. Italian freeways therefore work like parking garages where you pick up the ticket when you enter the garage and then give the ticket and pay to the parking attendant when you exit. At the exits there will be multiple booths. Some (yellow sign saying Telepass) are for people with the Telepass transponders (you probably won't have one), some for credit card payments only (blu sign saying 'carte'), some for cash only (white sign with money bills and coins logo). Not all of the booths are manned, many are now automated. Only cash booths may be manned (but not always). If manned, just give the ticket to the attendant, then the money according to how much you owe, just like a parking garage. If it's an automated cash booth, you would insert the ticket in the machine first, the machine display will show the amount you owe, at which point you insert the euros (bills and coins).
The cash booths that are automated have a logo that shows bills and coins only. Those that are manned have a logo with also a black hand holding the bills.
Some automated cash booths also accept credit cards (in that case the white signs will have also the cards logo under the money logo). Once you pay all the money you owe, the barrier is raised and you can exit. Your segments shouldn't cost more than €25-30 in tolls each. The automated booths give you change, so you don't need to have the exact money for the toll).
Below is what the booth overhead signs look like:
http://www.autostrade.it/it/il-pedaggio/pagamento-al-casello

Regarding lighting on the roads, that is no different from America. Roads outside of built up areas aren't generally lit (that is true also for American interstate freeways in the middle of the countryside). However rental cars come equipped with headlamps.

One more thing. Many Agriturismo houses are in the middle of farm fields where it's very dark at night. You might need a small flashlight to walk from the car to the entrance door. I use the flashlight of the iPhone or also a small flashlight keychain.

www.viamichelin.com can help you calculate tolls or choose routes that avoid them. Siena to Sorrento by the main highway, for instance, they estimate €83.

Thanks very much Roberto! I really appreciate your detailed replies... you have helped me out so many times with all of my questions and for that I am very appreciative! ps. I live in Canada :)

Great tip Laura! Thank you :)

If you are from Canada, then maybe you are not familiar with toll freeways at all. I don't remember seeing any in either provinces I visited (BC and Quebec), just toll bridges.

Regarding the toll from Siena to Sorrento mentioned by Laura above, the toll is nowhere close to €83. That amount on the Michelin guide must include fuel. The toll would be applicable only in the A1 segment from Bettolle (Valdichiana entrance) and Castellammare di Stabia on the A3. The toll for that segment would be €28.40.
From Venice to Siena, the toll applies to the Segment from Mestre to Firenze-Impruneta. The toll for that segment is €19.50.

Now that you know the exact toll charges, you can be ready to use the automatic self service booths, without worrying about getting the change back.

Thanks... I will have my exact change ready!

We do have 1 toll highway in Canada (it's in Ontario) and it uses a transponder which is mounted on the front windshield (for electronic billing) for provincial residents ... other users get a pic of their license plate snapped as they enter and exit the toll highway and then weeks later they will automagically receive a bill in the mail to pay their toll charges :)