Quick update. We managed to tow the Expedition 2500 miles without any issues in our travels this summer, all in all a successful DIY and the Expedition tows great 4-down. There were a few times that we had to run through the Neutral Tow enable/disable 2x to get things to the right state - but it was almost always because we didn't follow the check-list exactly (sometimes hard to get the timing right w/ the push-button start to turn off the engine but keep the car "on").
One thing I did have to add that I didn't realize when I first posted was a Brake Relay Kit - so that the brake function wouldn't mask the RV turn signals flashing the rear lights (since there are no dedicated turn signals on the Expedition). Basically the brakes being applied by my Air Force 1 system keeps the brake lights lit - so that when the RV is flashing the turn signals you instead get a constant "on" light at the rear - not what you want when you are slowing down to turn.
So this Roadmaster 88400 bake relay system : https://smile.amazon.com/gp/product/B003VASGIO/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 will help you fix that - it makes it so that the brake lights only work when not being towed. The relay gets 12V from the motorhome to indicate you are in tow mode. The kit tells you to take power from the light pin on your wiring harness - but I instead used the charge line I'd run to keep the Expedition battery charged while being towed. I also added a 3" of strip LED lights (under 1amp) under the dash that glows when there is 12v power from the charge line so i can tell that everything is connected properly and I'm going to get the brake / turn signal functions desired.