Brittany advice

Hi,
Dinan is a great call.
Further west, I like Quimper, a pleasant town which gives easy access to beautiful coastline (Crozon, Fouesnant), villages (Locronan), inland areas (the hills north of Pleyben).
For a third base, I would suggest somewhere close to Golfe du Morbihan, a beautiful bay with islands, with the Neolithic site of Carnac nearby. But I'm less knowledgeable about towns in that region.
Or somewhere around Lannion, near the beautiful Côte de Granit Rose.

We are looking at Vannes or Pont Aven in addition to Dinan.

I've been to Dinan and have stayed in both Quimper and Vannes. I think they are all nice places to stay. However, I was not driving and cannot say anything about dealing with a car in those towns.

Eleven days will allow you to cover Brittany pretty well with a car. I assume you're aware that April is likely to be coolish and dampish; it's not the time of year I'd choose. However, I'm much more focused on weather than average, and as someone who never has a car to escape to, I like to keep cool spots like Brittany to use as escape hatches in mid-summer.

I, too, have stayed in Quimper and Vannes. I was on a Road Scholar tour and we spent the afternoon in Dinan. The day we happened to be there there in late April there were a number of HS groups visiting so was very crowded. I, personally, enjoyed Saint-Malo more than Dinan. I loved watching the tides change and seeing the paths out to the 3 islets emerge and become accessible. I liked Quimper as well. Very cool cathedral that has a veer to the left, lol!!

We stayed in Vannes to be near the Alignments at Carnac and the other Neolithic sites.

I thought Brittany was wonderful!

We stayed in St Malo inside the ramparts in a wonderful B&B and had Parkingmeter outside the Walls about 10 Minutes from the B&B.It was nice at night to walk the Walls and watch the Sunset and Tide changes.Dinan is also very nice, we Day tripped there, full of half timbered buildings.
Mike

Another vote for Quimper. We enjoyed the Old Town there, including the market. We also stayed in Morlaix (maybe a good base for your hike along the coast) and in Loudeac. Morlaix is an interesting town but we mostly used it and Loudeac as bases for day trips rather than places to explore on their own. We drove. I don't believe you could do what we did using public transportation. Some of the places we visited were well off the beaten path.
Brittany is full of interesting churches, monasteries, prehistoric sites, pretty villages, beautiful coasts and more. Some of our favorite things were times when we happened upon local festivals, watching entire communities, from very old to very young, joining in traditional dances. And lots of double cheek kissing.

We spent 4 nights in St. Malo and loved it -- much preferred it to Dinan -- hard to beat the ramparts the ocean, the islands you can walk to at low tide. Dinan felt very tourist trappy on our day trip.

Don't miss the neolithic sites around Carnac.

I spent 8 nights in Brittany this May, mainly focused on walking sections of the GR34 trail, and absolutely loved it. I was based in Perros-Guirec (4 nights) and Saint-Malo (4 nights) and both were great bases. Perros-Guirec was quiet out of tourist season and absolutely lovely. The pink granite coast is spectacular and the walking was fantastic. I was there without a car so took the train to Lannion (which I would have loved to have time to explore) and then a taxi to connect to/from Perros-Guirec. The public transit was very poor in that area (at least at that time of year) but there are taxis (best to pre-book). Because I was mostly walking, not having a car wasn't a big deal. There is lots of great walking right in Perros-Guirec and I used a taxi to go to Port Blanc one day and walk back from there.

Saint-Malo was a bit of a shock after that, full of people and day-trippers. But it was a fascinating town to see and a great base with really excellent transit links. It's easy to take day trips to nearby towns (Dinan, Cancale, etc) and to hop a bus to another town/village on the coast and walk there. I enjoyed seeing Dinan but I was happy to stay in Saint-Malo, both for the beauty of the ocean and the convenience of the town's amenities. Dinard would also be excellent.

April may be wet and chilly. My favorites - starting at MSM in Normandy:
1. Cancale - world famous oysters that do live up to their billing. Great views of the tide going in and out (boats either floating or laying on their sides) from a number of seaside restaurants.
2. St. Malo - nice walled city with a small sandy (as opposed to pebble) beach. At low tide you can hike out to some fortified islands that are part of the city's defense. There is a museum there but I didn't visit.
3. Dinan - nice medieval center (note: they had a fire in the center this year, never heard exactly how much was destroyed) and newer port area down the hill with restaurants.
4. Ft. La Latte - an old fortress that's been used for many things over the years but now shows as the medieval castle it was built to be. You can climb up to the very top of the dome where the flag flies. Great cliffs and swirling seas below the castle.
5. Lighthouse - near Ft. La Latte is a lighthouse on Cap Frehel. I'd recommend this for birdwatchers. The cliffs and seas are nice but the draw seems to be the massive amount of birds on the cliffs.
6. Parish Closes - I visited three towns further west that include good examples of a Parish Close (semi-fortified churches with primitive granite carved crosses). These are unique for someone who appreciates architecture, the towns are pretty sleepy - Lampaul-Guimiliau, Guimiliau and St. Thegonnec.
7. Locronan - This town has been the backdrop for movies and TV series. It's a very pretty town built from the same dark gray granite you see in the Parish Closes.
8. Port Aven, Auray and Vannes - I wasn't interested in the bigger port towns. They seemed too industrial for my taste. These three were all very nice. Port Aven and Auray are fairly tiny. Vannes is much larger but has an incredible medieval center with ramparts. The port in Vannes is larger too but made for private boats rather than commercial.
9. Carnac - can be reached easily as a day trip from Auray or Vannes. There are various megaliths, formations, small passage tombs and dolman in the area.
10. Cairn Gavrinis - my single favorite thing. It's a passage tomb that was discovered in the 1980's. You can only reach it by ferry tour from Larmor Baden. The ferry also gives you a look at the spectacular tides in the bay and circles a half submerged stone henge. The tour is all in French but worth it even if you're French isn't great. Hopefully they run tours in April.

I would just add that although Rennes is a larger city, it might be a fine start-end city for train or plane connections, and even though it's the big city out there, the old center was a lot more fun to stay in than I thought it would be. Also, we found Dinan great as a day trip and St Malo ended up being our home base. Meanwhile, having one or more crepes, butter caramels, cider and/or un petit cafe every day wore out my stomach, but it can be great fun testing one's intestinal limits. And April might be wet, windy, and chilly, but it was like that in June too. C'est les temps à la Breizh.

Two small towns I enjoyed day-tripping to from Rennes: Fougères and Vitré. That was in the summer of 2017, and there were few tourists. You could probably see both well in one day if you didn't mind the driving--about 75 miles for the loop.

In addition to Dinan (or St Malo), to get a good overview of Brittany you could choose 2 other bases.
One could be further north west : along the pink granite coast, or near Roscoff. Or maybe near Crozon if you enjoy hikes and coastal landscape.
A last one could be on the south coast : Quimper, Concarneau or Pont-Aven depending on the size of cities/towns you are looking for. Or more central near the Gulf of Morbihan : Vannes, Auray, Trinité sur Mer... You could also choose to stay on one island for 1 or 2 days. You may get some ideas for places to see on http://visite.bretagne.free.fr/index.php/en/itineraries.html
For such a 11-night stay, it is better to rent a car (at least for some days, especially during your stay in western Brittany), it will give you more opportunities to reach small towns and beautiful places along the coast.

If you're looking for a good B&B, we enjoyed
Chambres d'Hôtes
26 rue de la 101e airborne, 50500 Carentan, France

It was some years ago.
I booked them through Booking.com and I just went there to find the B&B name/address and Booking says the B&B no longer accepts bookings through them. ? still in business ? Very nice house and hostess.