1.) Endless.
2.) Endless.
3.) Hm, probably Zidane, Quina, Freya, and anyone else that can use the '9,999 damage' attacks.
4.) Not really. The challenge is rewarding, though. I think it only has like 8 more attack power than Ragnarok, and it doesn't have any abilities unique to it.
5.) In the 50s, I believe.