Is this a doable one-day trip, since we need to start and end at st. remy, and need to tour st. remy as part of the day? st. remy-carpentras-vaison, and return?
And if it IS doable in one day, is it also doable to add any additional town on the way back from vaison to st. remy?
We did a day trip from Uzes to Vaison, which is about the same distance as St. Remy to Vaison. We went to the Vaison Tuesday market - which was great - and on the way home we had plenty of time to visit L'Isle-sur-la-Sorgue. We were back in Uzes in time for dinner. If you get a reasonably early start, your itinerary will work fine.
It's very doable. Be sure to see Les Baux as well. Don't worry about "touring" St. Remy. There's not much to "tour". It's a wonderful place to hang out in, though.