The Bree-mount uses a separate system from the level 35 mounts and should not be confused with them. If you have bought the gold edition and applied the item code to your account you will have a Bree-steed item in one of your inventory bags. Once you have done the bree-mount quests (available at level 25) you can exchange the item for a Bree-mount. You don't have to pay any additional price for a Bree-mount.
Once you have a Bree-mount the only thing you can exchange it for is a Bree-mount of another type. For example if you chose Bree-pony and your character is an Elf or Man then you can exchange it to a Bree-horse.
In order to get the festival mount you have to buy a level 35 mount first. That costs 4 gold and 220 silver. Once you have your level 35 mount you have to barter (trade/exchange) it with the vendor. You will receive a receipt of purchase when you do so. Once you have the receipt you can barter it plus 6 festival tokens and 1 festival run token for the Festival (harversmath) mount.
Do not sell any mount that you have. Once you log off you will not to be able to get it back and it will be lost forever.
Do not destroy your tokens. The same applies. You won't be able to get any more. Unless the same festival happens in autumn of this year.