Is there an official deck size for your objective and terrain decks for tournaments? Do I bring one's that I want to play, or just all I own?

The Tournament Regulations document (found on the Runewars Miniatures Game product page, in the Support section, or right here ), changes a fair bit of the game set up from what is in the Learn to Play and Rules Reference documents. If following it, the Objective and Deployment played by everyone in a round are chosen randomly by the Tournament Organizer from a set of 3 of each.

You bring Terrain cards, and their corresponding terrain pieces, as part of your army building. 4 cards, the total capacity of any 2 of which cannot exceed 6 trays.