Originally Posted by Daynn
After I got 3500 faction for one successful parley, I was able to play 10 cards.
That was only possible with an old charcter, starting to play diplomacy again after its revamp.
Anyway, to really answer the question: Before they redid the skill gaining pace I have personally had 7 cards, got one during the 'starter dip line' and the second one probably a bit after.
Don't expect to be able to play 6 or more cards anytime real soon, because the starter diplomacy quest (which is really long! expect to be spending some 8-10 hours also depending on how fast you manage to find everything and learn the card game, get the hang of things) leaves you at around a skill of 40-45ish. It's still a way to go to 100 then. By the time you can hold 10 cards you'll be an Embassador and it's at the maximum skill you can get, so that's basically the 'top level' of the Diplomacy sphere. Think of how long it takes to get to the end in Adventuring and you'll get the idea of time to be invested. :P