First, let me recommend getting the EL version, especially if you have a family and want extra cargo room.
The air ride vs. not, what does it take to convert to traditional spring? Are the perches the same, or?
There are kits available to do it and I do NOT believe you have to change the perches.
Transmission, the expedition is heavy, how is the transmission cooling?
I know you said you would not be towing with it, but I still recommend a transmission cooler. The (OEM) cooler itself can be found on eBay at a very reasonable price. It does require some additional houses and brackets to install. If you ever have to replace the radiator, there is a heavy duty version that bolts in. If you get AWD/4WD, the CYA step is to change the fluid between 75k-100k.
Is there a MY cut off for new vs. old style heads on the 5.4 like F150? This was june of 2007 IIRC in f150.
According to Wikipedia the date was 10/9/07. Build dates after that should be god.
I'll probably be shopping 07-10 MY as these fall within budget. What are common issues for these trucks with say 80k, 120k, 140k? I know enough to peep the common issues on the 5.4 and overall mechanical issues. Figure whichever one I buy, we will do compression test to make sure motor is healthy, new O2 sensors, new fuel filter and possibly a new pump when the blower is installed, ....
Struts don't last forever. You will have to replace them sometime.
(I have always wondered if the Nivomat mechanical self leveling rear struts for the 2015-16 could be swapped in to the older 3rd gen Expeditions.) If you are planning on doing the job yourself, I highly recommend taking the rear struts to a shop that has a heavy duty spring compressor. Those rear springs are HUGE !
IMHO, it is a waste of money to swap O2 sensors. Somewhere along the line, they stopped installing the replaceable inline fuel filter. New pump ? Fuel ? Oil ?