Could be wrong but 5sp on base model for 98 model only.
I would go for 2001 or 2002 year & not the base model;most likely less issue with oil consumption and/or manifold gasket failures. High end models have electric folding side mirrors standard as well.
Timing belt change due at 75k/100k depending on service(normal/severe).
Auto trans fluid should have been replaced/flushed per/or close to schedule.
Since it would be for light wheeling/camping only:
I would go for 265 AT's instead - better gas mileage to/from camps. Should be less noisy as well.
Shocks & springs from ARB/OME etc should replace the OEM ones. Just have to crank the t-bars to level.
Trooper comes with rear LSD so that should be good enough.
Locker up front, ARB bull bar/winch, sliders can be installed but should not be necessary for 'light' wheeling.

HTH