When I asked about the margin around an Icon, I was actually more interested in the Top/Bottom Margin, because...
a.) I think I already have a decent sense that you need "elbow room" between items
b.) Since this is for a Sprite, and since Sprites can be as big as you want and yet not take up actual space, I would think a person would want to be "generous" with the spacing between Icons on a Sprite, right?
But what about the Top/Bottom Margins?
One extreme would be to have No Top/Bottom Margins, and just have spacing between each Icon Left/Right...
That would make life easier when it comes to figuring out how big to build things. And I suppose you can always use Margins/Padding in CSS to give you more Top/Bottom room if needed, right?
See what I mean?