Hi Carey... I'm from Maine, too (hello islandgram!). A great restaurant within easy walking distance from the pier is Dimillo's. It's a bit "touristy" but you'll find lots of locals eating there because they serve great food. If you like baked stuffed lobster I hear from my husband that they make the best... get the crab stuffing on it. I like my lobster boiled. The restaurant is actually on a large boat so that's fun. You can sit and watch the boats bob in the marina while you eat. There are a couple of pubs between the pier and restaurant that are worth visiting, too.
The last time I went to see Portland Headlight there was a lighthouse keeper living there and they didn't let you in the lighthouse or their home (of course). But you can get great photos of the outside. There's not much else to see or do there, so don't expect much except a good look at a popular landmark.