What burning questions do you have that need to be answered?

For me:

1. Did Vecna choose Will or did the demogorgon take him for convenience?

2. Did the Upside Down exist before Vecna? 2a) If it did, was it populated by beings before Vecna? 2a.1) If so, who is really in charge of the Upside Down?

3. That "tube" that Vecna puts down Will's throat in the Upside Down - was it putting stuff into Will or taking it out?

4. How exactly did Brenner use Henry to give the other children powers?

5. Speaking of the other children, were they "special" or did Brenner just have easy access to them?

6. Is Holly hooked to one of those tubes, too?

I'm sure I'll think of more. I'm wondering what other questions people have. I'd also enjoy reading some of your theories on my questions!