Have you looked through the resources sub-board? There are a few characters written up, but I have no overview over that whatsoever.
Spirit Form is a must, obviously. After that, it really depends on what you want to do with him. Bob probably has all kinds of powers, which would be impractical for a PC to take all. He can do magic, though it's probably more a form of glamor than a form of evocation/thaumaturgy, in a way that it is an innate ability rather than an actual learned skill. I'm talking about the way he takes down the wards without breaking them, for example. Or how he keeps Murphy clear of the influence of the lords of outer night. Maybe a reskinned Glamour could work for something like this. The ability to directly manipulate magic, but with a few limitations put on it, to balance it.
Worldwalker is probably also in his skillset, or at least the knowledge part of it. Some knowledge stunts as well. Maybe a supernatural sense that allows him to perceive magic the way he does.
So yeah, a bit more background would be helpful, how do you want to play him, what niche is he supposed to fill in the group, where does he come from, etc.
Another way to go entirely, btw., would be something JayTee did in our game. His character met a dying spirit of intellect, and he allowed him to live in his head, in exchange for his help. Was a pretty cool concept.
