1) In dealing with the culling of LMB, one of the considerations is that the actual 'stunted' LMB already existing in the pond will never reach their ultimate potential size due to the lost years of growth when there wasn't enough forage. So, what would be ideal to achieve is maybe one remaining mating pair of LMB that when they spawn, those new LMB have plenty of forage to grow to their potential. I think you may have to wait and see how that works out, but in short, no, you should cull every LMB unless you see one that is more fat, larger or healthier than the others.
2) I would keep adding adult bluegill, but you always have to be wary of moving fish from one pond to another for various reasons such as transfer of parasites, or a different plant, or even legal issues.
3) I understand the concerns about feeding and creating more plant growth. Maybe there's a fine line where you could feed enough that the feed is not wasted, but you will have some excess nutrients from fish poo.
4) In the colder parts of the USA, you could have Smallmouth, Walleye, Yellow Perch, maybe some catfish and maybe some Hybrid Striped Bass. If you were to go with a new predator set up, I would seek to eliminate ALL the LMB in the pond, and that may also mean killing off ALL fish in the pond including all those Bluegill you've stocked.
