1. I can confirm the 64 and the 9, I have no idea about the 500...

2. Upgrades replace the base building, but you gain the benefits of both; the base building must exist before the upgrade can be built.

3. Can you clarify your question, please? building_present_min_level requires you to specify a building tree, a logic token (>, >=, =, <=, <) and a level

4. I think so, at least if I correctly understood the question.