I think you would be pleased with Colonial Gables since you don't want a B&B or a hotel room. I have passed this many times and they have a wonderful view and great location. The town of Belfast is interesting, small,uphill!!, good local food, and there are cruise charters out of the harbor (I have done this twice). If you need a hospital (we did) the one in Belfast is excellant!!! The homes in Belfast are very beautiful. Read about the history of Bayside and take a ride down their streets to see their gingerbread houses.
You can walk the shoreline from the town park that is next to the harbor. Everyone is very friendly, which is not always the case in some places in Maine. But I love Maine with a passion!!! If you ever want to go for a week or longer (longer is best) I would try to make it to one of the islands to stay, it's a totally different experience. There are diffferent types of houses, small to extra large!! All at different price points.
You will have a great time. I can't wait for Sept.!!!