Jeez man, the search function deserves a work out but here's the briefing:

The X went into pruction as a '00 model. Not every X has a limited slip rear end. Mostly SE models came with it, although there are some exceptions like the enthusiast package in 02+.

There was no factory locker option until the '05 came out. ARB is the only way for not on older models. Gas mileage stock is about 14-17 mpg in the city with a V6. All 4wd Xs were V6. The mileage with 32's or 33's will be anywhere from 10-14 mpg depending on whatever else you have on there.

Yes, with proper maintenance these engines can go to 300,000 although I don't think there's anyone on here with that high a mileage. The most I have seen on here was a bit over 150,000. they are still driving, however.

Yes, the X was offered as a diesel 4 banger but not here, in Australia. There was no turbo 4 banger or V6, however 2002 and up were available with a supercharger. Mileage with a supercharger drops about 2 mpgs from stock regular.

Have fun and browse the forums. There's a lot to read here.