4" is fine. Make sure to get gauges. Is it a K&N replacement element? Those are total trash, they leak. I have the Ford replacement but filters are expensive, if I had it to do over I think I would go with a Tymar type setup, The filter is huge, you can get them anywhere and they are cheap.
Any idea how old the Bully Dog is? How much does it smoke? You would probably be better off with a newer chip. I would stay away from Banks, they are okay, just overpriced.
Make sure you have gauges.
You should do the Hutch mod on your fuel system. That involves dropping the tank, puling the pickup and replacing the dip tube and replacing all of connections to the pump. The factory dip tube ahs a duckbill valve about halfway down that stays open and sucks air into the fuel. No good. People also claim that the connections on the way to the pump suck air, I doubt it but I replaced them anyway because I added a filter before the pump.
For oil any quality 15W40 diesel oil is good. I use Delo 400, Rotella T is also popular.