Ahhh MTB servicing/stripdown!
You'll be needing this website then
Sheldon Brown-Bicycle Technical Information
Sheldon Brown is a good general reference site to use - it's very informative.
One thing to watch out for on such an old bike is that you may not be able to get replacement parts for it if they are needed.
I'm servicing my Specialized Rockhopper which was built around 1992 and I need to renew the gear cassette due to wear.
Easy enough but for the fact that it's the original Shimano ultraglide system which was discontinued yonks ago!!!
As well as buying a new cassette I also have to change the rear hub to a Hyperglide to bring things up to date - so much for a cheap, inexpensive tidy up!! LOL!
As has been said, by the time you buy cassette removers, bottom bracket remover tool etc and if the wheels need truing, you may be better off getting a bike shop to do the overhaul unless you are going to use the tools regularly
Good luck!