I've done HHN alone before, and lived to tell the tale. Don't fall for the propaganda haha.
As for daytime trips, definitely try the small shows, like the various Harry Potter shows. No queue, and they're quite entertaining. Plus you can grab a quick bite and snack while watching.
Don't recommend Rock it or Hulk, as those require a metal detector, so you'll be without a phone for a big section of the queue. But try out Popeye, you sit in a circle, gives a great community feel. Or Gringotts, which has multiple pre shows.