Congratulations on the HSB decision! Using HSB as your apex predator (or one of your apex predators) will be a very great opportunity for you to teach others about this type of fishery. Having the smaller gape than the LMB and the very low likelihood of reproduction (never say never..) you will have a pretty fixed variable on predation.

With 400 YP you have plenty of opportunity for YP overgrowth so it will be good to have your HSB in the pond now to start preying on YOY YP in the spring. You didn't mention what size your HSB stockers were?

If the YP are 5-6" you could see ribbons this spring even if you don't stock larger YP this fall. The decision would then be, do you keep the ribbons and let the YP 'self-balance' with the HSB, or do you try to remove most or all of the ribbons to keep your YP in the 'hundreds' and not in the tens of thousands numbers for the growing season of 2018.

If there was a chance of a limited spawn from the YP next spring at ice out because few of the original stockers are mature enough, then that might just work out perfectly and you wouldn't need to buy larger YP this fall.

Having another growing season to keep filling out your forage and see how well the HSB due on their growth filling up on minnows would be a great opportunity. I suspect by next spring the 100 YP you just added now would still be too big for the HSB to eat?