I just rechecked chapter 37, page 17.
He delivered the potion to her that made her not age via mouth to mouth so potentially he absorbed some of the effect at that moment.
Do what ever you enjoy! There will always be people asking for More, More, More.
There there will still be other who appreciate you doing whatever feels right for you.
I think his health fluctuating near 0 but the poison never killing him is technically another Minecraft reference. Since Minecraft poison can't kill you either but reacts the name way.
I think they meant what he sold them and turned others into Nightmare Daywalkers too.
That's probably not how they work but he doesn't know that.
But without further testing he wouldn't dare risk selling them without knowing the repercussions.
I think that on the second page you meant to have it read as "And for what we were doing while staying inside" instead of "And for what we were during while staying inside"