Most storage sheds I've seen don't have any overhang. But you can certainly add one and use a panel to extend the roofing. Usually, edge flashing along the roof perimeter is sufficient.

It's ok to go about 9 to 10 inches neither too far nor too near but it just should be able to avoid water penetration in any circumstances.

I'd go at least a foot, You also have to think about water around the foundation, you also might want to think about drainage tiles along the foundation to avoid standing water. I'd imagine you could also look up building codes around your area or the internet to get a contractors advice.

always better to have overhang, but as long as it covers the top of the sides and doesn't allow water penetration it should be okay.

i built a storage shed and when we put the metal roof on it, the roofers didn't put any overhang on the side of it. so now, it doesn't cover the sideing. i'm concerned the rain will go down the sides of the building inside the sideing and mess it up. i want to reposition the metal roofing to extend it at least six inches over the sides even if i have to add a panel to cover it.