You can't choose when/if Odin appears.
At the end of the game I found that I never used magic. I had a good seed level, and all the gf's. I liked bahamut, eden, doom train, cerberus, ifrit, deoblos (miss spelled), and many more. I don't see why you wouldn't use them. A lot of things brings down your seed level but if you can answer the questions then thats not a problem. The only time I don't really use them is when I'm on disk three and have took time to junction many things with them. Like drain on status attack so I don't have to heal as much, or meteor or something for str so I hit for 9999. Hitting for that much can be a full cure each swing.
Sabin:
You think a little thing like the end of the world was going to do me in.
FF6
Barret
There ain’t no getting off this train we’re on
FF7
Seifer
"One of these days, I'm gonna tell ya 'bout my ROMANTIC dream!"
FF8
Marcus
"No cloud, no squall shall hinder us!"
-ending of FF9