I'm fairly certain you don't need to attack. And, no, I don't believe you can use the cards on that same turn. You'd have to wait for the next one.
At least I'm 95% certain that's what happens. I need to brush up on the rules some more. Then I'll get back to you.
Can you pass on an attack if you can do an attack, or can you pass? Also, if the attack results in your getting some cards, can you use them then or must you wait to next turn?