Hey.

I've got this client who's a dietician and wants a site with some functionality I'm not sure how to implement:

1. custom forms that calculate some stuff (like ideal body weight, based on a bazillion factors),
2. the user is supposed to be able to pay for the consultation with a credit card - which lets him access more consultation forms,
3. bi-weekly results from how a user's diet is going (weight reduction and so on) should be displayed using a series of charts, preferably in the user's account page.

I use Drupal exclusively, so the question is whether such functionality can be implemented using existing modules? Which modules would you recommend? Can this be achieved without writing custom modules (I've never written a Drupal module)?

Thanks in advance for your suggestions.