Welcome Jason,

What do you want to get back from the pond?

If you just want a CC hole, then you might have the makings for it already. If you want trophy BG, well that might be a different path. I wouldn't worry to much about them spawning, buy little ones every year to resupply the ones you take out. You have better control that way.

You mentioned growing bigger CC, if you feed the BG as RC mentioned, you will feed them in two ways, more and bigger BG and they will eat the feed too. Putting a tree in there won't necessarily get the BG larger, it takes food to do that. It might help more young BG survive, but if there isn't food for them they will stunt.