Re: Ebony Vs. Rosewood
In my experience, the difference is largely cosmetic. Ebony is generally darker, more consistent (the fretboard will mostly just look a uniform black) and ebony is smoother, and finer-grained. My personal taste leads me to prefer ebony fretboards, other things being equal, and I specifically sought out a used Jem7vwh which had the ebony board.
From what I've read, iirc, Vai uses a rosewood board these days, so if one is a Vai fanatic, maybe rosewood would be preferable.
I'm not sure what difference it makes in the tone of a guitar, as I have not had two very similar guitars, one with ebony, and one with rosewood, to compare, and even very similar guitars ("identical") can sound significantly different in any case. I think it boils down to what you like yourself, and it is largely a cosmetic decision.
That's my experience anyway. Others may feel differently.