Anyone spent time in Brittany?

With only 3 days it's going to be a stretch to see the places you want to see. My suggestion would be to stay in one place, maybe Dinan or that area. That would give you easy access to see Mont St Michel, St Malo, and a day for a drive around the Pink Granite coast. Then detour to see the menhirs on the way to Rennes. It's a lot of driving but I'd rather do that than pack up and move hotels every night. If you like to move around, then maybe spend one night on (or near) Mont St Michel, then one night in (or near) Dinan or Saint Malo, then one night on (or near) the coast, maybe Saint-Brieuc or Paimpol, then detour to see the menhirs on the way to Rennes.

We did a quick loop in May 2017. In addition to St Malo, we really enjoyed Dinan and Locronan. If you are into churches the elaborately decorated parish churches with their walled churchyards are very interesting.
http://www.finisterebrittany.com/parish-closes-brittany

We stayed in this restored weaver's cottage, location is remote but scenery is fantastic.
http://www.bnb-brittany.com/

I was not impressed with Vannes. Brittany is a wonderful area to explore, and we found it very uncrowded and untouristy. Enjoy

I liked Dinan, Dinard, Rennes, Fougeres and Vitre. I didn't get farther west than that and still haven't gotten around to Mont-St-Michel.

I have based in both Vannes and Dinan and covered a lot of territory from each, even as far east as Quimper. A lot of driving, but it beats moving every day.

as others have mentioned 3 days is not enough. last year we drove through a large part of brittany and our 'must see' site was the small island of ile de brehat. we hired electric bikes and toured around for half a day. having a car is almost a necessity for getting around brittany.
https://en.wikipedia.org/wiki/%C3%8Ele-de-Br%C3%A9hat
we stayed near and visited monte saint michel, it was very under-whelming. so touristy.

We spent 4 nights in St. Malo and one in Auray to see the Neolithic sites of Carnac and environs. We didn't have a car though. I thought St. Malo was miles more attractive than Dinan. It is on the sea with amazing deep tides and walking on the ramparts is wonderful. I loved coming back from the bakery to the apartment in the morning with breakfast bread along the ramparts. It is easy to get to Dinard, Dinan, Cancale etc from there and we walked to St. Servan to see the medieval tower which was a lovely walk. We loved Carnac. We spent about 6 hours touring the menhirs, a farm with a grave in the field and the Locmariaquer site and felt we had enough time. Wonderful place. Three nights seems way too short but would be possible if you focused on fewer things.

I have done a fair amount of Brittany, yet I feel like there is so much more to see. You will like Arromanches in Normandy. In terms of MSM, Saint Malo, the pink granite coast, etc., my choice would be to stay in Dinard. A quaint, perfect town and its quieter than Saint Malo and Dinan. I would suggest a day trip to Dinan. We also absolutely loved Locranon near Quimper and from there would recommend a few hours at the coast at Douarnenez. I think people have different needs/preferences/philosophies regarding travel. I don't mind changing hotels every 2 or 3 days, even 1 every now and then because I don't like backtracking and I like to cover a fair amount of ground. That said, we rarely drive or are in transit more than 2-3 hours a day. Now when my husband chooses to retire and we have more time, we will stay put a bit longer. I love Brittany, you will have a lovely time.