For what it’s worth, I have a ‘93 XLT with a 5.8L and the towing package. Back in 2005 I had a 2” lift, 33s, and Bilstein shocks. I put a Class IV hitch on it and towed a completely packed and very heavy 6x12 tandem axle U-Haul trailer from Jackson, Mississippi, to Tucson, Arizona. The chassis, engine, and transmission had no problems at all. The Bronco can handle more than you would expect, and I think if you are willing to take your time and not try to keep up with traffic, you should not hesitate to use it. In 2008 I used it to tow the same type trailer with just as much weight from Tucson to Brenham, Texas (about 1,000 miles). It did better than the moving truck we rented, which nearly got killed by bad diesel fuel. Over the past few years I’ve used it to tow a buddy’s 2006 Air Nautique 226, which is a huge boat. The Bronco is not happy about it, but it can do it. And now I have a 4” lift and 34s and 4:10 dif gears.
As for the air springs, they would be nice, but not necessary, as long as your shocks are decent.
As for towing in overdrive, it is not recommended, but I have done it a lot and my E4OD has held up just fine. It depends a lot on the conditions and terrain. I will admit that I am a bit of a risk taker.
I hope this helps, God bless your move, and don’t apologize for towing massive stuff with your Bronc.
Derek