This is my first Nishiki and I couldn't be more happy about it. I don't know a lot about them, but I know I have an Olympic 12 speed. The Serial number is KH11022. Does anyone know what year it is?

I believe it to have nearly all original parts besides bar tape, pedals, and possibly saddle/seat post. It is in pretty good shape. The rear cassette is worn and the chain slips so I will probably have to replace it. I replaced the chain so I know it's not the chain.

What other maintenance should be done to make sure it stays in working order? I paid $60 for it, was that too much?

It looks like it has:
Sugino RT crankset
Suntour drivetrain
Suntour Supurbe brake calipers
Dia-compe brake levers
Araya wheel set

Any thoughts on it?

(sorry the pictures aren't the best. I was in a hurry.)