Re: Amp question - wattage and tone?
The Legacy only has two channels, maybe he just needs a wider range of tones. Elcid is right, chances are you don't need either setup. I'd recommend a 2x12 combo, it has more than enough volume for any gig, and you can use it at home without the rest of your family beating you over the head with a baseball bat.
If you're going to for the legacy, keep in mind that you WON'T get Vai's tone without $10,000 of rack gear. Alone, and especially at low volumes, the Legacy sounds almost nothing like Vai. The clean channel is absolutely amazing (the best I've ever heard), but the lead channel has a lot to be desired.