Great bike and in very original condition. I've got a 1994 made frame which would have been 95 model year but with slightly different decals, but had the same stx-rc groupset as yours. Yours is 95 built so may have been late '95 model year or early '96 model year.
These frames were lacquered on top of the nickel plating (at least mine was), but I can't be 100% sure from the pics if yours is or not. I would guess it is lacquered over the nickel plate from your description.
It actually looks in pretty good nick, so I'd start with a strip down and clean and see how it comes up. If it still looks a bit rough, you may be able to polish it up ...which if it has lacquer may be best to remove lacquer first. The lacquer frequently flaked on these. On mine it had, and I'd lost some of the nickel finish too so had go for a repaint. I guess you could take lacquer off with nitromors, then clean & polish up the nickel plate with brasso or maybe autosol. The nickel plate on these does sometimes flake too...but my impression is yours seems generally to be ok.
To remove the chain...
Get a chain link extractor tool (e.g. http://www.chainreactioncycles.com/Mode ... delID=7962
). Change into smallest cog at the rear and smallest at the front. Now use the tool to push one of the pins in the chain out. This breaks the chain (though can be rejoined with a special pin after if needed). You can then simply feed the chain out of the rear mech & wheel. Probably best get a new chain. This one would be fine I think-> http://www.chainreactioncycles.com/Mode ... elID=42377
Regarding the bottom bracket, if with the chain removed you can turn the cranks by hand and it feels smooth and not gritty, and it has no side to side wobble then there is no particular reason to remove it. However if you leave it in place, be careful when cleaning not to get degreaser, soap or chemicals on it. If you do need to remove and replace it then you will need a crank extractor tool to pull the cranks off the bottom bracket axle and the proper bottom bracket tool to remove the bottom bracket. Probably worth getting a shop to do this in case the bottom bracket is really stuck in the frame, but tools are available. Crank extractor (you need the one for square taper axles)-> http://www.chainreactioncycles.com/Mode ... elID=32400
I think this is the correct tool to remove your bottom bracket-> http://www.chainreactioncycles.com/Mode ... odelID=689
As others have said, the most likely reason for the duff gear change you experienced is the grease in the lever has solidified. Could also be that your cables may need replacing. If you have proper bike strength wire cutters then you shouldn't have any problem with doing cable replacement, but electrical wire cutters usually aren't strong enough.
Re: other tools I'd recommend a headset spanner so you can regrease and adjust the headset if needed (bearing that the fork rotates on). I think this is the one you need (but maybe able to get cheaper versions from other brands)-> http://www.chainreactioncycles.com/Mode ... elID=78653
Whilst an adjustable wrench is enough to undo and also tighten the top locknut of the headset, when tightening back up you need quite a thin width wrench like this so you can tighten then hold it still whilst tightening down the top most nut onto it with an adjustable wrench.
By the way your handlebar stem is "sk8" your handlebars are probably the Orange "hot rod".
Happy to talk more via pm if it helps, but I'm away to bed now.
"1.21 Gigawatts !!! Great scott !"
Current winter retro steed - orange p7: viewtopic.php?f=6&t=60876&p=425424&hilit=p7+project#p425424
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