We went 3 times this last year, the final trip was for our wedding in July.
I read on here a while ago that everyone said "go to Mama's...you gotta eat at Mama's". It's now a guaranteed stop on every trip. Great food and you kind of feel like you're at a palce only Disneyland could have made. We go for lunch because there isn't much of a view at night. It's AWESOME!!
Lahaina is the big touristy area and you'll end up there more than once. I've done the submarine trip twice now and the last time we went we were bombarded by dolphin activity...it was VERY cool!!!
You'll have fun. There isn't much of a nightlife unless you're near a major hotel. Most of it is very low-key...kind of the Hawaiian way.
Low-key sounds great, especially after the past few months.