If you fish with live crickets then you should not add shiners to your pond. If you use artificials you won't have a problem. Shiners are good forage and help keep bass numbers under control by feeding on bass eggs. Don't worry, your bass will still have succesful spawns but the shiners can help keep their numbers from blowing up. Threadfin shad can fill the shiner role as a easy-to-swallow forage fish, I prefer a varied forage base just for diversity sake but threadfin won't survive my winters so shiners are a necessity for me.
Large bass will have the bluegill as their main forage item. Because bluegill are so tall they are hard for smaller bass to eat and that is where your shiners/shad help out. A 16"+ largemouth will eat bluegill with no problem because it can fit a 4-8" bluegill in its mouth but a 12" bass struggles to do that. Even large bass will eat plenty of shiners and shad as their shape makes them safer and easier to eat.
Are large brim (assuming brim = bluegill) a goal for you? If you would prefer large brim to large bass then increase your bass stocking numbers and you will have larger brim with more small easy-to-catch bass. You have an 8 acre pond so you can still get big brim with big bass but your stocking strategy would need to change to reflect that and your management strategy could be more involved. By stocking coppernose bluegills you will end up with some big bluegills (especially if you add a feeder).
