It depends on what your goals are. Do you just want to keep Darkside up? That's probably simple enough. Do you need to mitigate something with TBN? You could probably just keep a bit in reserve. Are you trying to save up for a burst window?

As far as cooldowns are concerned, there are some additional questions that you need to ask yourself. You may have noticed that you can't enter a combined Delirium/BW window with more than 50 blood. You also can't enter Delirium as LS is coming off cooldown with less than 50 blood. There are a number of little traps that you can run into that force you to cap resources unintentionally.

I'm very curious to see what the APM averages are going to be for the ex primals.

That being said, you're not going to have an epiphany on DRK by simply typing on the forums, any more than you reached an epiphany on why "defensive tanking" didn't catch on in raid content through forum debates. The answer then, as it is now, is to play it yourself and see.

As an analogy:
"He who studies medicine without books sails an uncharted sea, but he who studies medicine without patients does not go to sea at all."