Here's my take on this Jamaica; just my opinions:
Manufacturers usually suggest tire pressures in the low range. That gives a softer ride, less rattling and warranty complaints. You can probably go with 35 psi all around if you prefer a harder ride. At 38 psi it may be noisy and hard. Higher pressure will get slightly better mileage and probably handle better on the highway. It won't affect the alignment.
You should look up the Ford specs and watch the alignment process. See what camber the mechanic is getting. If it's out of spec, you need the kit, which is just a bolt and eccentric cam. It allows the top of the wheel to be moved in and out. He'll probably charge $150; his cost is $20 - $40 plus labor. If the camber is within the factory specs, you don't need it. If you need it and don't get it the inside or outside of the tire will wear and it may handle a bit squirrely.
The steering wheel should be centered. That's just adjusting the tie rod ends. That "toe" alignment which does this can also be a cause of your tire noise. They'll take care of that hopefully on the second go-around.
My Defenders on the 2008 are silent. My 2000 used to be pretty quiet too with Generals. It could be an alignment but it could also be just plain front end noise or what the tires do. You can read tire reviews on one of the tire sites and see if others notice the same thing on Expeditions and Suburbans. Try going down to the 30 psi and see if that helps too. The all-time 4wd versions made a bit more noise than the transfer case that was part-time. Any more than a hum could be a bearing, but that will let you know as the months pass.
Congratulations on all the work. Nice to have a good riding truck. Those early ones are fantastic. I miss mine every day.