I can't find this so maybe someone knows. Is there a maximumof a card in a deck and how many cards are required in a deck?

You get command cards based on the command value of your hero's. Right now, that's two per hero. You can not opt to take more or less, so in a standard 2 regiment game you will have 4 command cards. All of the cards must be unique.

I'll look up the page in the rule book and post it for you in a moment.

Rules regarding army building are on page 16 of the electronic version of the rule book, which is under the support tab on the Warhammer Diskwars main page.

http://fantasyflightgames.com/ffg_content/diskwars/support/WHD-core-rules.pdf

Thank you!! :-)