If we don't get a hotel room we'd plan to get in line at UO very early that morning before opening.
This is a good strategy. They will usually let you in to the park when it opens for early entry, but will then hold non resort guests at the front of the park. This gives you an advantage over all the other non resort guests who show up at opening time because you are already inside, and if they drop the interior rope early, you get an even bigger advantage. I usually recommend at least 30 to 40 minutes before official opening if you don't have early entry. This way you can go ahead and get maps, breakfast, bathroom breaks, locker rentals, etc and you are completely ready to go when they release you to the rest of the park. I'd plan on your husband dropping you off an hour before official opening. This will give you time to get through security, walk to the gate, get through the gate, and get oriented / ready inside the park.
Where is the best/closest/easiest place that my husband can drop us off that morning?
Citywalk drop off spot
For the castle tour, is there a separate line at FJ for that? Or is it basically the ride queue.
The tour is the ride queue minus the green house area. Basically, it is simply another line running parallel to the ride queue in the same area with a few exceptions. There are 3 main parts to the tour, with each section providing information needed to set the stage for the ride. The talking portraits, Dumbledore, and the golden trio all give little speeches that tell you the story of what's going on. They each have a couple of different versions of the same information, so it can be interesting to watch them cycle through their dialogue more than once especially if you walk in on them in the middle of their speeches. The advantage to the tour is that you can take time to actually here them. In the ride queue, you are constantly getting moved along, so you miss the preshow storyline. The tour also gives you time to really look around and take pictures since you can have your belongings with you for the tour.
Something else to check into, if you get there and he decides that Gringotts is too intense as well, ask if there is a tour only option available. A few weeks ago, I went with a friend and a TM told us to ask about this option. We did and were able to do the complete full ride queue minus the waiting part. It was really nice. I had no idea they offered this. Not sure if it was something they are testing out, something new, or something I just never realized existed.
Would doing this in the afternoon take a very long time then?
The tour is self guided, so it takes as long as you want it to take. You can walk through the whole thing in 5 minutes or spend 30 minutes rewatching the characters give their speeches. Also, if it is important to you ask the TM at the end if they can escort you up to see the sorting hat. The hat is technically past the tour only section, but I've had TMs offer me this option before, so depending on crowds at the time, you might be able to see that as well.
I'm also wondering about lockers/bags. Since we're not doing FJ or Dueling Dragons, I'm hoping we can avoid the lockers. I plan to do Gringotts first before any shopping. I will have a small fanny/hip pack on. Is that ok on Gringotts? It does have the 3 prong clasp that I've heard they look for. I know bags and stuff are fine on HE.
I'd just ask. If it isn't ok, get a locker. They really aren't that big of deal to mess with once or twice. The best thing to do is to really look around and go deeper in. People tend to congregate toward the front lockers, and it will look like there is a huge locker line. However, when you can go around the corner where no one sees, a lot of the time you'll find an open locker machine or at least a less crowded one.
What about Hippogriff? Can we bring bags / items on Hippogriff? Plan is to buy DS his wand before we ride Hippogriff. I've heard the lockers are too small for the wand boxes, so that is a concern.
I've never had issues taking things on this ride.
However, If your son can be convinced to part with his wand after you guys have finished with the spell spots, my recommendation is to send the wand to the front of the park for pick up later. This is what we do. Universal will hold purchases for guests at the front of the park, so you don't have to carry them around all day. Then you can simply pick it up on your way out. This way you can ride other rides as well, and he will have his hands free the rest of the day without you worrying about it getting lost or broken.