I wouldn't expect a small VC company to have that may engineers let alone an engineering culture, if they didn't they better be paying you hundreds of thousands to define one, especially since I'm assuming that you seem to be engineer #1.
> When I wasn’t working, I was too tired to do much of anything else besides basic life upkeep (laundry, making the bed, heating frozen meals, some sleep). My health started to degrade.
This looks like a serious red flag, are the other people (early founders and partners) also in the trenches doing this with you?