Magnets:
http://www.kjmagnetics.com/products.asp?cat=13
D11 would probably work just fine. The parts are plastic (and small to boot), so they're light. If you're worried that's too small, check out that webpage at a larger size.
Any typical Pin vice will work. I don't have 1 (i just use a dremel drill bit in my Black and Decker household drill with a steady hand) but checking out Amazon or Thewarstore.com should turn you some decent results. Don't pay anything more than $10, or you're getting ripped off.
As for color, that there stone looks an awful lot like "Fortress Grey." Maybe a hair lighter.
Prime normal Grey, basecoat Fortress Grey, Give it a very light drybrushing or edging with flat white (or slightly darkened white). Wash with a thinned black wash (or grey wash, with multiple applications, dependent on what you want for depth of color). You've been around a little while, do a bit of experimenting.