I currently own three E-Series (2 E250's, 1 E350) all with the 5.4 motor, all bought with minimum 140K miles. One was bought with 165K, it now has 264K; another bought with 203K miles, now about 285K. As long as proper maintenance is done to an accepted schedule you shouldn't have any major or super expensive issues anytime soon. If something needs attended to do it ASAP if reliability and a long life are your goals.
Oil changes with good quality oil and filter---I'm NOT a believer in all this high-tech stuff that's far more costly than effective. Of course I also believe oil/filter changes every 3-4K miles is mandatory; Valvoline MaxLife oil (Amazon @ $18/5 quart jugs), Motorcraft FL-820S filters (Amazon/eBay 12 at a time, about $3.50 each). FWIW I change oil "frequently" because I don't believe any oil is NOT subject to blow by fuel contamination, leaving it in the crank case too long just not a good practice, just IMHO understand.
Another key to drivetrain longevity is a transmission full flush every 50K miles or so---NOT the typical 5 quarts and a new filter service too many use even today. I've discovered its never too late to begin this practice---seriously consider it as a DIY job.
This guy wrote the end-all article how-to for this: https://www.ford-trucks.com/articles...-transmission/
That's a one-man/woman job if so inclined, I've done it by myself in my driveway without any problems. I shared my experiences here: https://www.ford-trucks.com/forums/1...ans-flush.html
While it might seem costly to keep a vehicle well maintained what does it cost in lost time, aggravation and frustration when something preventable happens? Most of us here can/will help with advise and sometimes actual how-to's on most any issue related to a van---always feel free to ask!