How many of each card can I have in my deck?

Soldier Cards - There is no limit to how many normal soldiers you
have, but we suggest not having many more than you have castles to
hold.  Our starter decks have 18 soldiers for 54 cards, and we feel that's
a pretty good start.

Hero cards - Only one hero per 12 soldier cards, including the hero.  
For example, if you have 15 soldier cards, you can have 14 soldier or
elite soldier cards, and one hero card (round down).  It takes 24 soldier
cards, including the heroes, to have 2 heroes in the same deck.   

Materials Cards - Up to you, different people have different strategies.  
Remember, you'll get them back (until you start losing castes, that is).  
No limit, as long as you obey the 2 to 1 rule (2 materials and special
cards per 1 soldier card).

Special Cards - When it comes to fortifications, castle cards, siege
equipment, and soldier, hero, and creature modifiers, it's really up to
you.  As for tactics cards, we suggest limiting the amount of a single
tactics card you can have in a deck before starting play; three maximum
usually works pretty well in our opinion, but customize it how you like.  
The game is meant to be flexible so that you can make it what you want.  
You don't need us telling you everything, do you?