The turntable should be easy to fix, it's most probably the standard lubrication issue of the lifting pin, shared by all B&O players that have the same kind of mechanism.
Sticky keys themselves are also a simple problem of cleaning them - the hard part is getting the front panel off so you can do it, and back on. Reserve plenty of coffee/beer/smokes, and keep any minors outside hearing range...
The power amp may have a blown output transistor(s), or some other issue - but it will need real electrical work (try both speaker outputs first, it could be only a defective speaker switch).
Dunno about the cassette, I have no experience with that (only had a BC2800).
All in all, you should at least negotiate a good discount due to the unmentioned problems - which doesn't help much though if it was a bargain to begin with. From what I remember, mine was a pretty good tuner and the amplifier is a well performing design as well. So the value in use is OK, but can't really say whether paying someone to fix it will be worthwhile. You could probably get a better working unit for not much money.