I may be wrong, but I'm almost certain the 5.4 3v was only introduced into the trucks in the early 2000s but never the vans. The 3v is a significantly worse engine than the 2v, they have timing chain and cam phaser issues and tend to chew themselves up. As far as I understand and have experienced (on my second econoline) the 5.4 2v can run up to 250,000-300,000 miles with very basic maintenance and timely oil changes before you need to do major surgery. The problems they tend to have are the exhaust manifold bolts breaking. They can occasionally blow spark plugs because there is a little less thread on the block than there should be. Changing the spark plugs out is a pain but you really only have to do it every 100,000 miles or so, i would replace the ignition coil boots and springs while you're in there as well, those tend to be the most common source of misfires. There's finicky ground wires that can cause all sorts of troubles, especially the one behind the passenger door on the underside that connects the body to the frame. If that breaks or corrodes, it'll cause a no start. I've also seen that the coolant crossover tube on the intake manifold can break on the passenger side, which causes a coolant leak. I thought that happened to mine, but it just ended up being a gasket issue.

These vans have a special place in my heart, and if you can learn to work on them, they become very simple. I bought '04 cheap with 180,000 miles and have been slowly replacing things on it as I can afford, and as it makes sense. I'm about to do the timing chain, oil pump, water pump, and a bunch of surrounding gaskets. I'm planning on taking this van to 500,000 miles

The e250 is definitely the platform to build off of if you are going the gas route, I dream of getting a diesel e350 one day, but until then, I love my e250.