Are there any important things I should do before...

[Vic_]

going off to the floating continent?

[Kraid]

There's not really much to be honest. You could always fight the 'super boss' of the World of Balance: Intangir (He's on Triangle Island and isn't really important but he's there if you want to attempt to beat him! You can't fight him after the Floating Continent.)

The other thing to do is wait for Shadow at the very end of the Floating Continent. There may be others, but those are the only two I remember right now.

[Vic_]

I was wondering about things like Lore that might be exclusive to the world of balance. I've only learned 2 so far <_< I was also wondering if there are any exclusive items that can only be stolen (by Locke) as well.

[Cor Leonis]

One of Mog's Dance abilities, Water Harmony/Rondo, can only be accessed in the Serpent Trench; the Serpent Trench is unavailable after the World of Balance.