The campgrounds are well patrolled and I have not heard of thievery should you take an overnight backpacking trip..
Because you have so many options I recommend getting a trail guide while you are at home
like this one..Starter not comprehensive
https://www.amazon.com/Hiking-New-Ha...rmat=4&depth=1
Huts for overnight camping are available but pricey. Tenting is allowed below treeline but must be more than 200 feet from the trail or water..There are limited tentsites.
Schoodic is a gorgeous campground.. Bike trails there too .. And hiking in the Donnell Pond area which is actually better than Acadia.
https://www.maine.gov/dacf/parksearc...ellpondmap.pdf
Campobelllo is a really small island.. We day trip there camping at Cobscook Bay State Park in Maine which is never full.
Camden is a nice town and part of the triad of three nice towns..Rockland Rockport and Camden..Parking is a hassle for many tourists.as they don't look down side streeets where parking is ample. Don't even try for the dock.. Mechanic Street is ablock away and has ample parking The OwlsHead lighthouse is very close as is the Transportation Museum.
You can try for Camden Hills SP..no hookups. Got time? Take the Laura B out of Port Clyde. 12 miles out to sea is Monhegan Island..Bring your walking shoes..Only vehicles out there on its dirt roads are work trucks. You can go for the day. Monhegan Boat Line.
Guaranteed you will have great memories of Monhegan over Bar Harbor( I detest that place in the summer.)