Z v ??: Optimal Amount of Broodlords per strategy

It's very dependent on what the opponent has and what you have. If they have a huge Tank/Thor army you can't really have too many Brood Lords, but if they also have 15 Vikings then you need to have Infestor/Corruptor support or you're in trouble. "Too many" just implies that producing the Brood Lords used too many of the player's resources and thus the army available to protect those Brood Lords isn't sufficient.

Generally, your initial wave of Brood Lords in ZvT should be about 4-8 against a Terran going Bio, but that's very adaptable depending on how the game is going- if he still doesn't have a Starport or if he's going Mech, you can be a lot more greedy. I'm unsure of exact numbers for the other matchups.