The answers to your questions all depend on what you mean .

If you mean that you would like to buy a new character slot for five platinum, that character will start at level one. You will, however, be able to keep your level 23 archer.

If you mean that you would like to delete your level 23 archer and start a new character for free, you will start over and lose all of your items.

If you mean that you would like to start a new character and buy him a premium pack, you will receive a special type of armor and a special hat. You will be given three of the hat and three of the armors. You will get one lv 1 set, one lv 10 set, and one lv 15 set (someone correct me if I'm wrong).