If you plan on putting bass in that pond, you DO NOT want to get rid of the blue gills.
The bullheads, on the other hand, should prolly go.
You need to get in contact with your local Ag Extention Agent and he may be able to help you out. He can send you a ton of info that your state publishes on how to manage private impoundments. It's all free.
I have managed farm ponds before and it takes alot of work and years to produce quality harvests.