Tuscany Itinerary - Help! :)

You ask why seeing Tuscany is so hard; it is a large area!
We broke it into several different regions on different trips. We spent four days in Florence and four in the Chianti region on our first trip plus Rome and Venice.
We loved Chianti and have returned there three more times staying in Panzano, Castellina and Radda. . We also have stayed in Cortona and Lucca. I would not stay in San Gimignano as it is a tour bus mecca. Visit it and leave.
We have returned to Florence on day trips too. Two full days, which is three nights would give you time to visit the highlights.
Your option 2 above will give you nearby access to the villages in Chianti too. You are trying to see too much.

During an anniversary trip a few years ago we split time between Florence and driving around the countryside. In retrospect I wish we had spent much more time motoring around the rural areas and less time in the city which we thought was something of a congested mess compared to our previous visits. We found ourselves looking forward to day trips to surrounding towns by train just to get away from the crowds.
That said, staying in or near Florence would allow you to shed your rental car a few days early, and would be central for trips up to Fiesole (a favorite), Lucca, Pisa, Montacatini, etc., and then the train to Venice to conclude your trip.
All in all, my wife and I are of the opinion that you really can't spend too much time exploring Chianti and the Val D'orcia.

Since you are going to Venice afterwards, it would make sense to return the car in Florence 2 or 3 nights before your transfer to Venice by train. For those couple of nights you would stay in the city center of Florence. That way you have at least one full day to devote to Florence, assuming you want to see Florence at all. You can also steal a night from Venice. Three nights are generally sufficient.

First of all Florence is about art, in museums, in churches, in public places. (I include architecture as part of art.). I can hardly think of another place on the planet so drenched in important art. If you aren’t interested in art, give the tourism-overwhelmed city a break and don’t go there. There is so much to see in Tuscany that you will easily fill your time elsewhere and be totally satisfied with your trip.
There are some wonderful day trips you can do from Venice, Vicenza and Padova being my favorites. If you do some and include visiting the islands, then 4 nights is not too much.
Btw, neither Florence nor Venice has a “city vibe” in the way Rome or Milan does.

A travel guide that we found to be particularly useful for our own driving tour thru Tuscany was "Backroads Northern Italy" by DK publishing. It not only features a number of off-the-beaten-parh scenic drives but also contains info on some of the lesser known attractions that other guides don't mention. We found it to be a valuable planning tool in sorting out our own trip.
You can usually find used copies for a few dollars on Amazon.

Thank you everyone so much! Each of you truly provided valuable advice for me. I just went onto Amazon and purchased the book you suggested @Robert!

I agree we are trying to see too much, which is why I think we should dedicate 12 nights solely to the countryside (nothing about staying in Florence appeals to me - Lucca and Siena are more our speed) so that we can find our favorite areas and do a dedicated vacation there. I did set two days aside to just follow our hearts, maybe I should set 4 aside for that! 😂 We do plan to visit many more times, because we are quite certain we are going to fall in love with the Tuscan countryside and want to return repeatedly. After reading your advice I am thinking Pisa, Lucca and Cinque Terre might have to be a whole separate trip. Thank you again for taking the time to help provide input!

If you’re thinking about visiting Florence and maybe Lucca and Pisa but are worried about staying in a bigger city, what about spending the 4 nights in Lucca? It’s an easy train ride into Florence when you want to see the sights there, but much lower key and oozing with Italian charm. I spent 6 nights total last summer in Tuscany (Volterra/Siena/Montepulciano) and loved it. I did stop through Cortona and didn’t find it as interesting as the towns in Tuscany. However much time you spend in Tuscany, make sure you get in as many drives as you can. The parts between the towns are the most amazing.

I would have to recommend Lucca also. I have spent three weeks there twice in the past (at a language school), and will be there again in May. The city can be explored well in 2-3 days, but there are many interesting places in the area that are excellent locations to visit.
Lucca does lend itself to a slower speed; at that time of year the tourists are few, and the weather usually perfect for sitting on the wall with a picnic lunch. Florence, Pisa, and even the Cinque Terre are easy day trips. Lucca would be a great opportunity take a vacation from your vacation. Have fun!

Tuscany is vast and has SO much to explore. I spent 6 months in Florence 2019 (dual citizen) and was never bored. It is a busy city but so much to see and if you rent an apartment in the right neighborhood (Santa Croce/Sant' Ambrogio neighborhood is my favorite) away from the main attractions, it is peaceful. Many day trips also possible from Florence as a hub....Bologna, Parma, Modena, Arezzo, Cortona, Lucca, Sienna, Greve and others in chianti area. Even a day trip to the beach (Viareggio) is a fun day. I have found in planning my 2022 6 month stay that as much as I love having Florence as my base, rentals have gone beyond my budget so will stay in Pistoia which is only 30 minutes away and will save a ton of $$$ and still be able to visit Florenc and some friends frequently. In my humble opinion, 4 nights in Venice is probably 3 nights too many. Whatever you decide, it will be magical...enjoy!