Omega Weapon ain't impossible if you played card games and you got the right cards to exchange with useful items. I think it's very useful for you to get the Laguna Loire card if you want to beat Omega Weapon (I think you can receive this card from Ellone in disc three).
As for the Final Boss, well, it's a very long battle, at least for me it was, but the best suggestion I can give you is to equip each single character with equal number of magic spells and GFs and don't have only Squall at 9999, but also all the other characters or a t least some of them
. I didn't know the strategy of the enemies (they won't let you choose your team, they randomly pick the members of your team), so I only equipped Rinoa, Selphie and Squall and Quistis and Irvine got killed in a couple of turns
