We liked Villa d’Este and with adding Hadrian’s Villa, Tivoli is a good idea. There’s not that much else in the town, and technically, they can be done from Rome on public transit. Heat and sun can be issues at Hadrian’s Villa, as well as maintenance closures of specific parts. We spent a few hours in the historic center of Viterbo on the way to Orvieto and our hotel near Sinalunga. Started in Civitavecchia, however.
It is important to add traffic and other congestion’s into pure map driving time estimates, even on controlled-access highways by highly skilled American drivers. You are wrong to dismiss Orvieto purely for off-center timing reasons. You could even consider Caserta, because Positano is somewhat ... remote. Ostia Antica?