First of all, Congratulations on getting married!
You can get from your spot in Freeport (get on 295 at exit 17 which is the closest to your hotel) to Downtown Portland within 15 minutes. It's an easy, breezy, traffic free drive directly on 295. It won't be a problem at all. Get off at exit 7 ("Franklin Arterial/ Route 1") for downtown Portland. You can Follow the Arterial for about 2/3 of a mile and you'll come to Commerical Street. Park anywhere here and wander of into the Old Port.
There are numerous restaurants worth trying in Portland. Bresca, Grace, Fore Street and Hugos would likely form my top 4. Fore Street usually requires reservations a few days ahead of time. Grace is located in an old Church just off of Congress St (on Chestnut I think?) and it is very pretty inside. It would be a great place to enjoy a romantic dinner. Bresca is a more intimate setting... only a few tables. Fore Street is a rustic/casual atmosphere but also has nice harbor views from the back of the restaurant. Hugo's has (in my opinion) the best food on the menu, but the least enjoyable atmosphere... it's really tasteless inside (sort of an attempt at modern rustic).
I would suggest taking the the ferry to Great Diamond Island or Peaks Island. The
Casco Bay Lines serve these islands. If there is any way you can bring a bicycle with you (or rent), that would be an excellent way to see the islands.
If you're into art, check out the Portland Museum of Art. It's one of the nicer small art musuems I've seen.
in additon to the Old Port, I'd walk on foot around the West End Historic District as there are some nice homes to be seen there. The Eastern Promenade is a great place to explore too.
No trip to Maine is complete without Lighthouses. I would certainly go out to Cape Elizabeth and check out Fort William State Park/ the Portland Head Lighthouse. It's (I believe) the most photographed lighthouse in the nation.