Florence side trip

I have not been to Lucca, but we did Siena and San Gimignano (and Pisa!) on a day trip from Florence last year. I think for most folks, 3 days in Florence is adequate (yes, many will think you need a week or more but most of us don';t have that kind of time). It gives time to see the big museums, and to wander around. We had 3 full days and while we could have enjoyed more, I felt like it was a good taste of the city. We loved the Tuscany day trip, and with 4 days, I do recommend it. I have heard Lucca is nice. We liked Siena quite a bit and also liked SanG, although it was smaller, and rather touristy. I'd look at the RS Italy book and see what there is to do in each place that might appeal the most to you-but for a day trip, almost anywhere in Tuscany is going to be nice.

I have been to all 3. Depends on your interests. I love Siena and Lucca, and have stayed in each twice. San G I just found more touristy, was only there as a day trip, though. Check out some youtube videos. The towns are all so different.

Depends on your interests. You can hit the big sights easily in 3 days, be sure they are full days though, that means 4 nights. It means 5 nights if you are going to spend one day outside Florence.
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David, Bargello, Uffizi, Ponte Vechio, Pallzao Vechio, Boboli Gardens, Pitta Palace, Piazalle Michelangelo, Santa Maria Novella, Santo Spirito, etc. All in 3 days shouldn't be a problem.

I would always add 2 days to a trip to Italy if I could, you should too.

Lucca is an hour away by train, Siena is a couple of hours, San Gimi is more problematic. The train is in Poggibonsi then you have to get to San Gimi from there. Bologna is a possibility as well. We spent a few days in Montecatini Terme and Alto, cute place too and on the way to Lucca.

Siena has the most to see of those three destinations and I find it well worth one of your 4 days in the region. Get an early start by bus or train to make the most of it.

Thanks for the input.