Welcome to Pond Boss, VApo!
Adding regular strain bluegill is a good idea, and trying to get bluegill over 5" is the right line of thinking.
How big are the LMB now? You might need larger than 5" bluegill.
Relocating fish from one pond to another is generally discouraged by some experts here mainly for the risk of transporting some potential fish disease to your pond. But, many pond owners to catch fish in other ponds and relocate them to their own.
Some say you can minimize the risk of disease by putting the fish in a salt bath in between transport between ponds.
