I think I'm stuck

[Treize]

Also, did you do Yuffie's sidequests yet? I like to do her sidequests right away. That way you could level up a little, get some good materia, and get it done so that you don't have to do it later.

Yeah, I think at this point you should be able to use Regan to cut down some of the healing that you should have to do, but you'll probably have to have someone as a full time healer because the boss does a lot of damage. Maybe you might want to build up your limits beforehand against some other monsters and go in prepared. It could help.

Edit: A couple HP Pluses could help a little too. You won't be using much magic, so this could boost your stats up some so that you shouldn't die as easily.