I originally had plans to disable units so you can control calamity and retrieval, but it did present various design and balance issues. But I might add a ritual that puts a unit to sleep/meditate for a bit and after it wakes up it's temporarily empowered, or something like that.
Selling buildings does not offer a lot gameplay wise, but it does introduce some issues I think. Maybe just selling units, but maybe the biggest annoyance here is that you are forced to always have miners in your build. So maybe the solution is that after first prestige you no longer need to build miners to unlock other buildings/units. The reason you're forced to buy so many miners now, is so that new players are led to have good production and do not get noob-trapped into buying too many non-productive buildings early and then end up having bricked or super slow start.
Indeed. I will add the display of upgrade requirements. Probably after you buy them once, they become revealed for following runs.
Thank you for the kind words and feedback!