Brad,
From what I know, blue gill will not usually eat minnows. I have been told they eat insects, larva, and other small things. Adult bluegill have little mouths, they might eat minnow fry but I don't think they'll eat an adult fathead. Also, I do not believe it takes two years for them to spawn. If the conditions are right they could possibly spawn the same year you put them in the pond. If your trying for a bass pond, I have been told the key is diversity. If you don't have any bass in your pond now, stocking the smaller blue gill won't hurt you. If you do what that one guy said and wait a year before introducing your bass the bluegill will be well established. The ones you but in should be too big for the bass to eat, and there should be plenty of small ones or fry for the bass. Over time what you'll find is that the bass will have eaten all of one size bluegill. For instance, you spend a morning throwing a net or a small sein, and you'll see lots of bluegill fry, 1-2" bulegill and adult bluegill. This is because to a bass it might take two or three 1-2" bluegill to equal a 3-4 bluegill. Sorry I kind of rambled. I hope that helped a little. Good luck