Apart from any custom handbuilt frames (and I may, of course, be wrong) I'm not aware that US or UK bikes (mtb or otherwise) generally had frame saver lobbed in them. So to that extent, they're all potentially prone to rust. My '02 Orange P7 doesn't, and a mate's 95 or 96 Nickel finish P7 didn't either. Even a handful or more years ago Brant Richards (On-One blokey) used to recommend just rinsing the frame tubes round with engine oil in the event that anyone was that worried about corrosion on their frames.
I'd guess one of the worst but inspectable places on the rockhopper is likely to be at the bottom of the seattube - water gets chucked up by the rear wheel and some of it ends up there. (I used to have to empty out my ~89 'dale after every wet ride, despite the fact that the seatpost seemed a close fit). I guess have a good look down - likewise in the headtube, BB shell etc - with a torch and see what it looks like.
Re old suspension forks - yeah, you'll have trouble finding anything worth riding, or at least anything you want to ride regularly and not care about, IYSWIM. The latest early (if that makes sense) decent ones that you might find relatively easily would be Rockshox Mag 10 or Mag 21.
http://en.wikipedia.org/wiki/RockShox
- those'd be 1" (not sure about ahead or threaded...I'm sure there's a wiki somewhere). If you *can* find any old Pace forks the elastomers will almost certainly be stuffed - my mate with the P7 gave up on his ~2001 or so (my P7's the one he replaced it with) because they were knackered and he couldn't get replacements - even from Pace. By 96/97 they'd move to coils/damping cartridges. I've got a set of those (MXC I think, 60mm or 70mm travel - there was a long travel kits which added 20mm) on a '96 M2 Stumpjumper, I think I bought the forks in 97 (I bought the M2 rigid).
I'd stick with the rigid forks - they were intended to have flex anyway, not up to today's sort of riding but probably fine for an awful lot - I did more than a few trailquest events on my 'dale. Even any rigid forks you can find nowadays with disk mounts are probably going to be too long axle>crown race (istr there was a 'standard' length of about 420 or 440 mm - try measured that on your frame and see what you come up with - if you want I could measure my old rigid 'dale and see what that is, that *definitely* predates suspension).
V -brakes would be decent upgrade tho' (the parallel-push XTRs are/were some of the best - you can still buy them but they're not cheap) - but Avids or LX/XT should be good - it ought to be possible to find some on
ebay for not a lot.
If you've got to buy wheels anyway, it *might* be worth buying them with rim brake rims and disk hubs if there's not much £ difference - if you then buy another bike with disks you've got a spare set of wheels.