Hi from Wisconsin,
As you might know Brittany is big, as in long. You might decide to rent in three locations. Brest is at one end, duh. Staying there means all touring is in one direction. Better to be more centrally located. so 15-20 miles in two, three or four direction is possible. Also, no matter what you choose, if you get too far off the main roads it can gobble up driving time to get onto the 'big' road. Then again, prices and beauty often increases as you get off the main road.
Have you tried gites de france. It is a real clunky French website that rents cottages. To request English go to the slashes in the upper right of the opening page. But you type in Bretagne or some other city in Brittany and start scrolling through the dozens of places for rent. A bit like Vacation Rental By Owners (VRBO). Both of these can find you really interesting places to stay at around $200-600/per week. Select cottages with bed sheets. It is long story why many cottages come sheetless. Rentals are set up to be Saturday to Saturday. Out of main season you can get fewer days at a time or to arrive on a day other than Saturday.
Really, you have plenty of time to select cottages from either of these websites. We had one of our best times in a Gite in Normandy. Owned by an English woman who had inherited the farm. Be patient with the website. Bretagne is a word used for more than Brittany.
wayne iNWI