It has no oil filter. Change oil after 1st 20 hrs and then every 100 hrs or annually. Use 15w-40 diesel oil or straight 30w if you only use it in hot weather. It ships from the factory with 15w-40.
Air filter depends on the severity of service. While driving, annually will probably do. Dusty conditions, more often. I blew mine out and got two years out of it.
Welcome to Lake Wobegon where Justin and David utilize abductive reasoning to help solve F/SS issues.
Happy Trails and Remember the Pequod.