Which parking lots and scenic routes would one suggest for a Siena - San Gimignano - Pisa - Lucca circuit from Florence?
This Rick Steves guidebook should help you plan: https://store.ricksteves.com/shop/p/florence-guidebook
Use motorways as much as possible, the ordinary roads are very curvy and slow. The only execption, from S. Gimignano drive Castelfiorentino-Empoli on the ordinary road and then take the motorway at Empoli for Pisa.