We enjoyed a Brittany trip several years ago. After flying to Brest for a couple days, we rented a car there, and headed out. It’s on the coast, due west of Dinan, but it’s a big city, and less charming than other places in Brittany.
Farther south, Quimper (aka Kemper as well as Quimpair) was a fascinating Renaissance town, although it’s a bit inland from the coast. Same with Pont-Aven, where many Impressionist artists were based, long ago. We had memorable stays in both.
Nearby is Concarneau, on the coast, a nice town where we also stayed.
Last, Lorient was good, a small city on the coast, and from where we also did a two-day guided sea kayaking and camping trip to the Isle de Groix.
If you can, on your way from Dinan, stop off at Josselin, a medieval village with a fairytale castle.