There is no "season" for fog. It rolls in just about anytime in Maine. The last two summers, the fog has not been too bad. Most days were sunny with good visibility. You need a good GPS chartplotter to keep you out of trouble. I don't have radar and manage pretty well picking my days and staying put when there is no visibility.
As far as anchorages on Penobscot Bay, you will need a couple months to explore them all. Some of my favorites are Holbrook Island / Ram Island just outside of Castine. Travel up the Bagaduce and you will find more spectacular places. Try Warren Island in Islesboro. It is a state park as well.
You must sail through Fox Island therofare. It splits North Haven from Vinalhaven. There are nooks and crannies to drop a hook there. Don't miss Isle au Haut. Beautiful hiking trails and home of Linda Greenlaw. There is also a group of islands between Isle au Haut and Stonington. It is obvious on your chart and a great place to spend a night or two. Stonington is a fun place to explore but not a good anchorage since it is so busy with lobstermen producing a lot of wake.
Spend a night in Pulpit Harbor, drop your hook behind Butter Island and row to shore to visit the sheep, find Horseshoe Cove and see if you can navigate inside, don't miss Buck's Island in Brooksville and don't miss Brooklin where you can drop a hook at Wooden Boat. They have a dock that welcomes visitors to walk their grounds and visit the boatbuilding shops.
For provisioning on Penobscot Bay, it is hard to find a better harbor than Belfast. EVERYTHING is there for a boater including laundry, library, hardware, marina, pubs, groceries, movie theater, etc. All within a half mile walk of the harbor. You can usually get a couple free hours of dockage at the public docks, get diesel, water and pumpout.
Camden is also a great stop but harder to anchor. Rockport has very little and Rockland also has everything you need.
It will be a memorable summer for you. Enjoy.