1. The Tomb of the Unknown King. As soon as you get Minotaur's Card.
Unless you can get to Dollet before that (someone recently brought it up, but I don't remember being able to go back there before the trip to Deling City), then sounds about right.

2. Odin.
Yep.

3. Mug Ultima Weapon, and defeat Omega Weapon.
Well, the mugging Ultima Weapon may be a loop hole (depending on how you define "consistently" in this context). There's another way involving a side quest involving no fighting in which you can obtain a Three Stars. But I'll count it if you answer the last question correctly.

4. There are many. Ultima and Protect, Firaga Blizzaga and Thundaga, Ultima and Life, Ultima and Shell, Ultima and Full-Life... As long as you can absorb Fire, Thunder, and Ice elements you are ok.
The Fire, Thunder, and Ice part is what I was looking for. You got it.

5. 5, I think. Quistis, Zell, Diablos, Ifrit, and MiniMog.
You're missing one.