First question! Yes, Davesprite can be his ghost-self. We leave exactly how well the phasing works up to your discretion (for example, if you wanted to have him knifed, you could say that the Arena is making his powers glitch out or something, but we won't demand that as a limitation). Our only hard and fast limitation is that he cannot exit the Arena, and the laws of space (e.g. no gravity, no oxygen) still apply.

Your second question is more complicated. If Davesprite's ability to magic things is like Sailor Uranus and her Space Sword (i.e. attached to her soul and unable to exist independently of her), then yes. However, if he's just magicking random things into existence, then no. We're willing to work with you a little bit on this, but this cannot be used as a means of just hoarding items.

If you have more questions, please ask.