Well, if you need pre-ground beans it's really not gonna make a huge difference where you get 'em from, imo. For the best coffee you wanna grind 'em immediately before making the coffee. The Black Cat espresso (roasted by Intelligentsia) at Manic/Darkhorse/etc is really great, but they'd probably cry if you asked to pre-grind for espresso.

That said, you're probably better off with pre-ground coffee rather than using a whirly-blade grinder. But any other coffee nerds, feel free to speak up. I actually invested in a fairly expensive (by most people's standards) coffee grinder, but I still just use a fresh press and a moka pot (like what you have) at home.

As for the amount.. just fill the filter overflowing with coffee, give it a few taps to make sure there isn't any empty pockets in there, and then just use a knife (or something) to push the overflow off and make the top level. They don't recommend tamping (squeeze the grinds in) for moka-pots, generally. I guess because they don't create enough pressure to get the steam through the coffee.