(( I mean the new units, the 2 veteran and 4 priests. Because unit wise don't the priests typically get assigned to specific units individually to give the widest impact?
Still reading though the info ( shees this is gonna take months ) but don't Priests, Psykers and Commissar typically act as field commander type things beneath the general? ))
No, Priests, Psykers, and Commissars are placed on a per regiment basis however the Psykers and Priests are to follow the orders of the Highest Ranking Regiment Officer (in this case you) though the priests generally have a larger say and control in what they do in battle due to the fact that they'll know how to do their jobs better then you in most cases. As for Psykers they are kept on a short leash and follow your orders pretty much without question in most cases.
Commissars however are different, they exist outside of the normal IG Hierarchy so they only really answer to Generals, Lord Militants, Warmasters, and other high ranking officials. They are the IG's discipline force so thus they can't (and won't) follow a low ranking officer's orders (like you).
As for moving the priests and veterans, I'm sorry but that is a no. The veterans are their to act as the Ministorum Priests personal guard and their escorts so they stay with them, and the Priests themselves will go to where they are needed in a battle (though you can command them if you wish) so they are in their own little detachment. They're attached to aid you in a warzone, but for all intents and purposes they are Ecclesiarchy members to the core.