I would say off, but there may be some that would be well suited for competitive play. Of course I don't know if this is meant to be a more serious tournament or a just for fun one.
Items are competitive. It's stage interactions that aren't, We need a challenge.
Well it will depend on how they play out. They aren't in Smash and very well my not be in All Stars. Will just have to wait and see. Some may be, but no way all will.