It's a beautiful time of year to be in Maine. I live about 50 miles inland from Acadia and have been there many times. You'll have lots of company since it's a popular spot, especially now. Traveling the roads at peak times can get frustrating so you might consider travel times (early morning, week days, etc.) that will minimize the traffic.
The popular spots are worth seeing, Cadillac Mt., Thunder Hole, etc., but there are many beautiful areas just outside Acadia that might be of interest too. For instance, if you go back to Ellsworth and take a right towards Sullivan, look at a map and find Scoodic Point. Beautiful rock formations and a view that looks directly across to Bar Harbor.
Don't forget that most of Maine lies away from the coast. Most people who don't know the state think of it in terms of the images they see of the coast. But there are equally beautiful spots inland. For instance, if you were up for a day trip, you might consider going to Baxter State Park. And if you're really adventurous (you have to be) you might consider the hike up to Knife's Edge at the top of Mount Katahdin.
If you're sticking close to Acadia, do try the Lobster from one of the many roadside stands that cook them outside in sea water. Very informal and very good.
Enjoy yourself, it's a great place!
Best,
Tim
