I've dropped to 0/0 stats before w/an rs. The energy bar goes completely empty and doesn't rise until you put in a dorm mate.
If they have misc or any stats at all, you can still hit them depending on the bonus. One of my alts dropped stats to 0/0 and hits were able to go through lol
Yes, with no energy. I remember since I couldn't drop a cat I had on the account but a friend was able to hit the account lol. Idk how it works, just does.