Florence/Tuscany

Two nights only gives you one full day for Florence. Is that enough to see what you want to see? It seems short to me, even if you do not see all the museums and churches. Then you spend at least half a day going to a new place, checking in, getting oriented, and have one full day to enjoy it before moving on to the Cinque Terre. Make sure you have a solid plan for Florence (what does everyone want to see and do) before you decide 4 nights is too many. You can easily take a day tour (Tours by Roberto) to see some countryside.

If you're looking to stay at an Agriturismo, it needs to be worthwhile, the whole point of staying at such a place is to relax, slow-down and absorb the area...which means 3-5 days minimum, otherwise, it's just a waste and an inconvenience to the owners. If others in the party have never visited Florence, 2-days won't be enough. You need to figure out if you want to be a country mouse or, city mouse, if you want both, you're gonna need to adjust your schedule.

If you're fixed on such a schedule, I'd spend some time in Lucca, about half-way between Cinque Terre and Florence. Charming rival to Florence, it's one of the last of the walled-city's of Italy (Ferrara being the other). Personally, I think the food in Lucca is better than Florence, ask the locals and they attribute to the better surrounding farmland, which results in better produce, not to mention it doesn't get as humid as Florence in the Summer.

One full day in Florence and one full day for rural Tuscany? That is not enough time to see either of them.