I've not been to Siena on a Sunday but it's possible that this will be the case in early April. Does anyone know if I can expect many shops to be closed and is there a more limited bus schedule, to and from Florence? Thanks.
We went on a Sunday in January from Orvieto. It was very crowded and one place we ate at closed by 4pm. There were a lot of things open when we left after 6pm
You can sample the bus schedule on the company website
http://www.tiemmespa.it/index.php/Viaggia-con-noi/Acquisto-titoli-di-viaggio/Biglietterie
We took the Siena-Florence bus on a Sunday last spring; as I recall, there was diminished service, but still multiple options.
Trains are also an option on Sunday if bus times don't match your schedule. While the Siena train station is less convenient than the Siena bus station, trains run with reasonable frequency from early moring to late evening.
Thank you, everyone! Good information.