Forgive me if this is a stupid question or if it has been covered someplace else. I haven't seen anything about this so I figured I would ask.

Is there a rule against putting more then two factions in the same deck? Can you have 3?

Also is there a limit to the amount of cards in a Deck? I know the minumum is 50 is there a Max?

You could have 7 factions in your deck if you like. It makes it difficult to resource smartly if you have too many factions, but nothing against it.

Deck minimum is indeed 50, and there is no maximum. Note that the more cards you have in your deck, the lower the probability that you will get the card you planned for. So in competitive tournaments it is almost always exactly 50 cards to maximize the chances of getting the good cards.