Tim's right that any excess oil from over filling gets deposited in the airbox but these engines are heavy breathers (crankcase fumes) and naturally as the crankcase breather is fed directly in to the airbox, you're gonna get a build up of oil.
As long as it's not sloshing around and overflowing the levels in the bottom of the airbox, you'll be OK.
With the standard airboxes it' s best to check and clean it every few thousand miles or so.
PS. Keep tinkering, it's good that you're getting to know the bike. Things have a habit of coming loose and falling off these bikes, so always best to check them over on a regular basis.
