Some good advice given here... I too agree you really need to hammer the LMB. Those 4" sunfish will be expensive food as has been said. While you are thinning out those LMB, I would work on putting more cover in for the few BG that are having a remote change of making to a 2"... Christmas trees, etc sunk in 2'-4' of water should work well. The addition of the tilapia should help take some of the pressure off your BG population. If you can pay more and get guaranteed 6"+ RES or BG, get less but bigger fish to add. 6" BG should be safe from 12" LMB if your pond only has bass in that size range... 3 acres is big enough to make it a challenge to keep up with the LMB reproduction, so enlist all the friends and family you can to help you out...