To answer Joan's questions:
1) I would agree that "mazel tov" is the appropriate greeting for the card. If you need a mazel tov stamp, let me know, and I'd be happy to send one to you for you to borrow.
2) If we (meaning me and DH, not Jews in general!) give money as a gift, we always give in multiples of 18. It's in no way mandatory, or inappropriate if you don't, but if you do, it will show that you've given some thought to the symbolism behind it.
mnhyrkas -- I have two bat mitzvah cards in my gallery
. I used "girlie" colors in them, as opposed to any sort of "traditional Jewish" colors, which for some reason people seem to think are blue and white. I guess that comes from the fact that the Israeli flag is blue and white? I do love using blue and silver for Hanukkah cards, though -- I think the colors look so pretty together! I think I have a Hanukkah card with those colors in my gallery, too.