No specifics, as whilst we've stayed in the area, we stayed inside towns/cities, or in the case of Siena, a decent but somewhat characterless 'resort' apartments about 2km outside the city.
On the whole we've found agriturismo.it to be good / accurate, and there will be plenty of options listed. Another that has far fewer listings, but what it does have is typically very characterful - Alasdair Sawday / Special places to stay.
Other thoughts:
- April not too bad for daylight, but we tend to avoid driving in the dark, so might seek an agriturismo that has an apartment, or at least somewhere where we can store & prepare some food. In this way we might have the big meal of the day out and about, followed by a late afternoon passeggiata, returning to the accomodation before dark, and grazing on some light cold food in the evening. If it's a night the agriturismo is doing food, that might get reversed, eating light at lunch.
- Driving into anywhere remotely large can be stressful, especially with the threat of ZTL fines, so I'll typically prepare a route to the intended car park the night before (with a back-up as well). It just gives that little bit of confidence / awareness of the roads.
- Siena disappointed us, but perhaps my expectations were too high. Montepulciano was good, and feels like a day trip where you'd see enough to make it feel worthwhile. IIRC car parking near the bus station is good (and gives you the shallower walk into Montepulciano), but maybe also worth parking at San Biagio and walking up. That sharper incline will be decent exercise and it's a nice way to emerge into the town. La Grotta restaurant (opposite the San Biagio sanctuary) impressed us.
- Colle val d'Elsa was a good little day trip for us (also taking in our traditional visit to a nearby Decathlon sports superstore). It felt less touristy than Siena for sure. As a centre for glass production, maybe that might appeal as well?
So all a bit general I'm afraid.