The sheath issue has been hashed and rehashed here, there are lots of references to it around here. Even if the you had to toss the sheath and get a new one right off the bat, the knife is so good it would be worth it.
I have a BK9 which I have removed the coating from. Once I used it to remove a branch from a swimming hole and it took a dunk in the river. Now, I never bother with oiling my blades, even the naked ones and the BK9 is no exception. The bare steel got wet and I merely wiped it off on a dry part of my shirt and stuck it back in my custom kydex sheath. When I removed it a little while later I noticed a little bit of moisture in the sheath and on the blade but I didn't worry about it. Anyway, that uncoated knife that I have never taken any care with at all has never rusted at all. I don't clean it or oil it or anything other than sharpen it and so far have not had any problems. It is worth mentioning though that I live in a fairly dry climate and rust isn't much of a concern here. A more humid region might be different.