The orbits that are most useful for our current-day satellites are crowded, of course, but you could stash your asteroid booty anywhere you like. Putting it in orbit around the Moon might not be a bad move.
Earth orbit isn't that crowded. And you don't need to spread out. A cube of 100x100x100 m would store plenty of metal, but would not need more safety margin distance than any other satellite.
It is pretty crowded, actually. We've had satellites literally colliding with each other before. Filling it up with chunks of asteroid isn't the best use of limited room, especially when space farther away is genuinely empty and since you're coming from outside the Earth/Moon system you can put the goods anywhere you want.
All kinds of interesting processes become feasible in weightlessness. For instance, some kinds of alloys just aren't possible on earth because the metals' densities are so different that they don't mix properly. No so in space.
The orbits that are most useful for our current-day satellites are crowded, of course, but you could stash your asteroid booty anywhere you like. Putting it in orbit around the Moon might not be a bad move.