Minimum 20 000 000 hz to see something from the forge process. I'm kidding.  You can buy the amount you will want and then lease you coins to one of pools which forge. It is not recommended to forge yourself from your account with your bought amount. Needed really to much hz to earn something. The earnings from forging are not to much even with leasing. And are much few than the bounty you will have for the same amount you will buy.