UPDATE: (2018-09-11) EME have decided to also merge CH into TR+AV.
NOTE: This form assumes that the number of characters on each server equals the number of character slots used. If you deleted characters in the past, or if you used slots without creating characters, you may have additional available space. There's no way to check this right now except to try creating characters. If you are a regular F2P account, you start with 2 slots on each server. Founder accounts have 8 slots on each server. Also, be sure to check your Item Claim and inventory/banks in case you have any extra Character Slots lying around.
* NOTE 2: The free character slot items you receive are permanent (non-tradeable), and you can use them at any time. But if you want to receive them, you have to login between that time and the merger.