The Lincoln Navigator L is an excellent choice. The Ecoboost engine has been around for a few years and I assume is reliable. The L model is definitely better than the short version, because you actually have good space behind the third row seat (similar to comparing a Suburban to a Tahoe). Having Andy do your setup is an excellent idea as he focuses on that every single day, so he is a better resource than the average weekend warrior internet expert.
The only possible negative is that I understand Lincoln recommends mid grade fuel (???) for the Navigator, and the same engine in the Expedition is set up for regular unleaded. I might be wrong, but that is what I recall from a few months ago when I looked into it. Of course, that might not bother you at all, but I wanted to mention it.
Regardless, the Navigator is an excellent choice.
