Open recruitment section. What is the number than I must insert on section: Required might >= ?

This is the minimum might level that players need to have to apply to join. It's up to you and will depend on the general level of your state, this might be under 1 million, 10 million or 50 million. Check your own might level and decide what might is appropriate. If you are a new alliance and want to attract new members you can set this low. But if you are looking for the best of the best then keep it high.