Glad you've found your way to the New England forum,
hitherandyon, despite
InkUnderNails claiming that Maine is not in New England.
I agree with
BearX220, DO make reservations. Memorial Day weekend is VERY busy in Maine, with it being the rather unofficial start of the summer.
If you're looking for sort of "quintessential" coastal places to go in Maine, I would recommend spending time in Kennebunkport, Boothbay Harbor, or the Camden/Rockport area. If you're interested in scenery that does not involve the ocean (but beautiful nonetheless), I would highly recommend a drive up US Route 201 to Jackman, and over to Greenville from there on the Trans-Maine Highway. There are places to stay on Moosehead Lake, which is a popular destination (and again, I would HIGHLY recommend a reservation there).
Portland is a great city and there are myriad dining and entertainment options in the downtown area, especially in the "Old Port" area, roughly the area between Commercial Street and Congress Street North/South and Central Street and Franklin Street East/West.