It would be highly unusual for a half-orc to be allowed to be a cleric in any standard Darokin church. More likely, the half orc would be a member of one of the underground churches of the Demons (Alphaks, Demogorgon and Orcus) who are the patron immortals of the humanoid race or Thanatos (Immortal of Death and Doom. aka. the Archfiend). For more information on playing a cleric of this type, consult your DM.
Congratulations, you have now successfully created a Mystaran character!
For further development of this character, consult your Dungeon Master.