For the cam chain, the answer is "it depends". Some chains are worn out within 5 or 6 thousand miles, while others have seen over 15000 before needing service. If oil changes were infrequent, the bike idled for long periods or saw extended periods of high rpm use, use of oils with low zinc content, etc will affect cam chain wear rate.

The oil leak sounds like the infamous head plug leak. The fix is either take it apart and reseal the plug or get the Versy o-ring head plug that eliminates that problem entirely.