you can simplify the card scheme as well by offering different prizes for different hands.
say you offer a $5 amazon card for a 3 of a kind
$10 for a straight or flush or FH
$20 for a 4 of a kind
$25 Straight Flush
$50 for a Royal
Make it a monthly contest so members will be encouraged to earn as many cards as they can get.
If you limit the max amount of cards to say 3-4 a week per person, the work load and odds will be in houses favor. Also to reduce workload, award cards on a weekly achievement basis.
1 card awarded per week for 15 posts
1 card awarded per week for participating in 5 or more days of trivia
1 card awarded for downloading a casino ??
1 card awarded for posting a top 10 score in an arcade game
1 card awarded for logging on all 7 days
1 card awarded for winning NFL contest
1 card awarded for correct guess of contest
ect ect