For comparison's sake, I recently rented a 10x10x10 ft. storage unit for $90/mo. or $0.09 per cubic foot per month.
2) Amazon has an inventory control system. You can request certain quantities of items be sent back to you at any point, for cheap.
3) Amazon allows you to use their marketplace as a way to get rid of the stuff, so your average storage costs decrease over time and end up being much less as long as your stuff sells.
No, as you will gain nothing from it.