So I inherited 2007 Mercury Mountaineer with 190K miles and a replaced 4.0L 6-cyl engine. Know nothing about its history, nor why the engine was swapped nor the miles on the "new" engine.
This is the primary issue. All vehicles wear out but in this case it depends on how many miles on the replacement engine, whether it was (probably) used and how many miles on it before swapped in (if you can even trust what a junkyard/etc tells you about original miles), and whether (HOPEFULLY) new timing components where put on if not more.
Suppose it only had 100K mi when swapped in, new timing components put on, then you could be good for another ~150K mi from that point forward, or until the tranny fails. Replacement tranny could cost more than vehicle value, but it could still make sense if the rest is in good condition. I never expect a rebuilt tranny (besides Motorcraft crate) to last nearly as long on 2nd tour of duty. When the timing chain rattle at cold startup, starts, you typically have more than 10K mi. before it fails. Not always but we can only play averages.
Definitely take the seats out of they'll never be used, though you may then decide that you want a coated/covered plywood section added to level out the cargo area