I think a BG/LMB would work just fine for your goals. The little guys will soon be able to catch BG in your pond. As the Boys get bigger, the BG and LMB will also be getting bigger. Your timing should be almost perfect!

You actually need both the BG and LMB together to keep each other in check.

A channel catfish only pond (or with redear sunfish) should also work for you. If you feed the catfish commercial food, then they will gain weight rapidly and the kids will have quite a workout in short order.

Do not try to eliminate the crayfish. If you introduce LMB, they will feast on your crayfish!