We will be taking a coastal Maine roadtrip in the next couple weeks. I already have our accommodations booked for all but one night.

Night 1: This is the only night I don't have booked. We will be driving up from NYC so I'm not sure where we'll end up. Possibly around the Kennebunkport area.
Night 2: Rockland
Night 3: Rockland
Night 4: Bar Harbor
Night 5: Bar Harbor
Night 6: Bar Harbor
Night 7: Portland (early morning flight out of PWM)

We are a family of four (all 21+) with one in a power wheelchair. We enjoy beautiful scenery, local food scene (seafood!), easy hiking trails, a little shopping, and charming small towns. Not really into museums or beaches. Might be interested in a short sailing/boating trip.

Would love to get some input on the most quintessential Maine coastal towns to visit, accessible trails in Acadia, and all can't miss highlights/stops along the way.

It's certainly not a time of year when one can wait until the last-minute to book something in the Kennebunkport area. Nearby, visit Cape Porpoise and Goose Rocks Beach.

Near Rockland, an easy walk would be along the shoreline fro downtown Camden into and around Rockport. Mt. Battie is worth a visit...and for a charming small town maybe stop in Damariscotta on your drive up from Kport to Rockland. Round Top Ice Cream for sure. It's one of the easier towns to access as some of the others require 20 mins detour down a peninsula and then 20 mins back up.

Southwest Harbor, Bass Harbor, Winter Harbor...you won't have any trouble finding quaint townships to visit from Acadia.

There are probably a few good seafood restaurants just a short walk from your Rockland hotel...where are you staying?

Port Clyde and Tenant's Harbor are charming small towns/villages near Rockland.

From Port Clyde you can take a boat ride on the old mail boat, and you can also take a full day trip to Monhegan Island. The Marshall's Point Lighthouse is also there.
Owl's Head State Park has a lighthouse and some nice hikes, as well as a small, unguarded beach.

From Rockland, there's the ferry to Vinalhaven - about an hour each way.

The mile long breakwater leading to the Rockland Lighthouse is a cool thing to do.

Less than an hour from Bar Harbor is the Schoodic Peninsula, a lovely, quiet area where part of Acadia NP is located. I preferred it to Bar Harbor as it was much smaller and less crowded.
In season I'm pretty sure there's a ferry between the two areas so you might look into that.

We just visited Marshall's Point Lighthouse. It's a great place to sit a spell and enjoy looking at the water. Also the Rockport marina is a fun place to watch boating activity. There was a sailboat taking passengers out. There's a food truck that parks there.

Both Waterman's and McLoon's are great small lobster shacks. McLoon's is in a more scenic location on a working harbor and has a larger menu. Probably one of the best lobster rolls we have ever had. Claws in Rockland as you're heading out of the city toward Rockport had an interesting menu but dh did not care for the amount of seasonings put in the soups. He got a lobster burger which he loved (and we had never seen before, think giant crab cake) while I got the sampler (small cup seafood chowder with lots of dillweed, small cup of lobster bisque with an interesting but non-traditional flavor and a crab cake). But, I don't recall if their small dining deck is handicapped accessible.

We have enjoyed the easy hike to Owl's Head Light but I don't think you can see the view unless you climb the stairs at the end. Agree that drive to top of Mt. Battie is great. Bring binoculars. We like to picnic there.

According to googlemaps, one option from NYC will take an hour longer but goes up through western MA to Brattleboro VT then to Concord NH. The next part is to take Rt 101 (boring limited access hwy) to Portsmouth. From Concord, if you take Rt 4 it is state highways over to Portsmouth and much more scenic. It will also take you past Wagon Hill Farm which is open to the public for hiking. I could not find any info about whether the main trail was ok for wheelchairs. http://hikenewengland.com/WagonHillFarmNH091004.html

If not, Hilton Park would be a good choice for a break from driving. We frequently made it a lunch stop when pulling a camping trailer back from Maine.

I'm not a fan of southern Maine but I think my choice for #1 night would be York. We haven't been in ages but there's a good sidewalk, benches and grassy area in the Short Sands Beach area. It is traditional to watch the taffy pulling machine at the Goldenrod otherwise the downtown area is mostly tee shirt shops.