I'm not sure I understand Adding things to your card pool. "Example: Xianghua's F:"

If I am to add an attack to my card pool:

1) Am I able to attack with it?

2) Do I have to check for it?

Also does (+X) mean I add progressive difficulty to the check "Example: Xianghua's E:"

1) I deal damage of 3 does that mean i have to check 4 since there is 1 attack in my card pool?

2) If I choose to fail the check does my combat phase end?

If you add the attack to your card pool it just sits there. You can't play it unless the effect says to do so.

The (X+) just means you have to make a check at X difficulty. Failing a card will only end your turn if it's a card you are playing from your hand as a form .