The 2000 Gen 2.5 has the the same drivetrain as the 1997-99 (3.5L SOHC, 4 spd auto, 4.2:1 rear axle) and same body style as 1998-99 (flared fender aka Gen 2.5). Only difference between 98/99 and 2000 is the latter was not offered from the factory with a rear locker. Locking rears from earlier models (Gen 2: 4.6 ratio, Gen 2.5: 4.2 ratio) are a direct fit. The larger diameter 4.9:1 rear from a Montero Sport can also be fitted to the full size Monteros (see Eurosonic's build).
There are a few trim levels. Low trim has cloth seats no sunroof. Mid trim has headlight washers, leather seats/sunroof. "Endeavor" trim has mid trim plus wood interior accents, Infinity sound system--it's the equivalent to the 98/99 "Winter Package" minus the locker. The only option on the Endeavor Package was 3-way adjustable shock absorbers. I don't know if 3-way shocks were available on the low and mid trim year 2000s.
The seats do fold completely flat.
The 3.5L engine is notorious for leaky valve cover gaskets and front/rear cam seals, which drip onto the exhaust manifolds and produce a burnt oil smell in engine compartment. These leaks can also ruin the alternator if bad enough. Along with replacement of the previously mentioned gaskets/seals, the vehicle will need timing belt/tensioner/water pump and spark plug replacement if there's no documentation of it being done recently. If it's burning oil at the tail pipe, the valve stem seals will need replacement, another common issue with this engine. It will also need the crankshaft bolt updated to the 3rd revision, as the first two versions are frequently known to fail. Last, the valve train is known to be noisy, so don't be alarmed if you hear a lot of ticking from underneath the valve covers.
If the vehicle has not been shifted into 4wd often, its common that the 4wd dash indicators will flash vs. stay solid. Often, this problem will fix itself after the transfer case is shifted/excercised a bit.
The Aisin transmission is a solid piece and not known to fail.
None of the above issues are deal breakers, mostly just maintenance items on a 15 year old vehicle. Nonetheless, you should be aware of them when purchasing and definitely use them to negotiate price. Monteros are well built and a solid choice. Good luck!