Aside from a few art magazines and printers who prefer 350 or 360 ppi, 300 ppi is the standard for a printed image. Decide what size you'd like it to be printed, at least width wise, and make your profile at 300 ppi and your set

24 inches would get you 7200 ppi. That's currently what I'm working on. 12 would get you 3600 ppi.
Of course if you're thinking purely digital, that's another story. :P