Yes on weight distribution. Along with maintaining proper ride height, most will help with sway, either as part of it's design or with friction plates, which is the big part of towing such a large item. Weight distribution isn't really required when towing something like a boat. Boat trailers have lower weight and are usually designed with the boat in mind so that it's carrying it the best way possible
With the travel trailer, you will find that you can easily and drastically change the load and how it tows by were you place items in the RV. Are you towing with full tanks because your dry camping. Are you having extra coolers due to an extended stay. Kids bikes, clothes, just the extras you drag along to support the RV etc will all change the balance. The weight distribution hitch will correct most of that and make it so you tow the same every time.
Trailer brake controller is very necessary as well. It keeps stopping distances reasonable and also maintains the life of your tow vehicles brakes. Your expedition is designed to stop it's full GCWR by itself, but you don't want to be doing that all the time. I couldn't tell you the name of mine. They all work pretty much the same. You'll want to see if you have the factory harness to connect, then you just splice this harness to the brake controller and it just plugs in. It's worth having this harness and not splicing directly into the vehicles wiring.
Tow mirrors are another item that you didn't really need before with a pop up but will be beneficial now. There are strap on ones at walmart or tractor supply that work fine. You'll be able to kind of see to the sides of the RV with just your factory mirrors, but if your in any amount of traffic then you'll want to be able to see farther back to be able to make a lane change.
Keep asking the questions, I prefer to know what to expect before I go. Then it can be easier to determine if I have a problem, or it's normal while on my trip.
Matt