Do the artillery and watchtower tokens go back to the reserve at some point or do they stay where they are for the rest of the game? Or once they are in a battle they come back to the reserve for future use.
I also read a early post that said if all are placed of one type and you can pick up one and use it somewhere else paying the cost. Is this correct?
They are returned to the human's reserve after they are used in a battle resolution.
And yes, if all tokens are already on the board you may pay the proper costs and choose one from the board to place somewhere else on the board.