Hey Katherine!
Sounds like you are headed down the right track. I do own a STR in York County, Maine that I am pleased with and am a real estate agent out of Portsmouth. Like others have said - I do see a drop off in the winter months. We use it as a STR year round and choose not to place a tenant longer term through the months of October to April.
I do think that the North Conway/lakes region market is a hidden gem in New England commanding year round demand with all of the attractions it offers. Because most of the people visiting Kennebunk/Wells/Ogunquit and York are coming because of the beach, rentals do die off after September. There are quite a few restaurants and shops that close up for the season that doesn't help the draw to the area.
Portsmouth, NH is a good year round draw and the shipyard as far as an employer does also help for someone looking for a more medium term stay. From experience, unless you want to put a longer term tenant in place from October to say May, I don't think you will experience 80% occupancy along the seacoast of Maine.
Happy to connect if you have further questions!