I haven't had rust problems, even with the stock sprocket. I do store the bike in a garage and lube the chain after a ride in the wet.
I have never bought a kit, always bought my sprockets and chain as separate pieces. I really like the DID chain in VM (my first replacement) or ZVM (what's on it now). While the ZVM is a stronger chain, I think the VM is more than adequate for stock and mildly modded B12's. I don't have enough miles on the ZVM to tell for sure, but I'd be surprised if it outlasts the VM by any significant margin.