The answer to your scenarios are very different. If you go CC free (kill them all) then you might be able to do a HSB, HBG but would then have to plan for who your new apex predator will be. Obviously you probably would not go back down the road of using CC as a apex predator unless you like to eat them.

If you can't remove all the CC or choose not to, then you have to selectively kill or remove MOST of them and can't really plan any other stocking plans until you get to that point. Also while the CC are being diminished (if you do the slow removal plan) the regular bluegill are going to be populating wildly so there will be a time where you likely will have to transition over to your other apex predator.

Is a drain down and complete fish kill a possibility or do you prefer to manage what you have there first?