Sounds like a reasonable plan and you will be in the middle and end of foliage season. The only suggestion I would have is to go to Bar Harbor first, about six hours drive from Boston. You could then work your way back. It will be colder in the north. There would be less tension concerning your flight if you ended your trip nearer the airport.

Things get pretty quiet after Columbus day the further north that you go, and weather can also get quite chilly in late October, even snow maybe.

I wouldn't book anything with more than a 24 hour cancellation notice required. Just wing it, otherwise you might have reservations at a bunch of places you never make it to, arriving in Boston with snow and cold predicted for the next few days.

This really depends on what you want to do at each stop The last part of October can be cold and dismal, like last year (snow on Halloween). If the weather is bad, Acadia might not be the place to be.
The Portland foodie tour is fun but it takes a good part of the day. If the weather is warm I would recommend either a Portsmouth harbor cruise or Portland mail boat cruise (probably need coats out on the water). It gets darker earlier but you're going to want to explore around Rockland. Check out the free wine tasting at Breakwater Vineyards? Tour Farnsworth Art Museum?
Foliage could be glorious in Camden and if it is, a trip to the top of Mt Battie via auto road is mandatory.
Your route will also miss some of the quaint harbors out on the peninsulas and some good places to stop for lobster.
Driving back to Boston in time for a flight on the last day would be nerve wracking to me and would depend on the day of the week.

Great thank you all for your suggestions! Starting in Bar Harbor does sound like a great idea and less stressful. Maybe we will try and scoot the trip up if possible otherwise I hope with how the weather is so crazy maybe all the seasons will be shifted later. Thanks again!

Keep in mind that Salem can get a bit crazy as Halloween approaches. It makes it fun (if you like that sort of thing) but also means bigger crowds, tougher to find parking, hotel rooms etc.

In Gloucester, Fort Stage Park is a nice place to get out and stretch your legs and climb on the rocks. Halibut State Park is another place to explore.

Just want to note that, although we do get a couple of flurries in late October once in a while, anything thing approaching a snowstorm (much less a major once) is not the usual! According to a local weatherman in the Boston area, there's only a one in three chance of even having a White Christmas.

As already stated, expect major crowds in Salem in late October.