Referral program: look up referrer with a custom field

Hi,

I'm creating a referral program with the flow below, and I have a few questions.

Our referral program flow (C= customer, L= referred lead):

1. C enters L's name, email address etc and C's email address in a form.

2. The form creates a new lead record based on L's name, email address etc. C's email address will be stored in a custom field called "referrer's email" (synced with Salesforce).

3. Marketo looks up C based on "referrer's email" and stores that C has referred L.

We need to have both C and L's information, as we will send different emails to C and L, and later we will reward C and L if L becomes a customer.

Questions are:

a. how can I lookup C's record based on "referrer's email" tied with L's lead record?

b. what's the best practice to collect the data of whom C has referred? Counting up the number of leads C have referred is not enough, as we'd like to communicate with them later. Also, we expect a C might refer several Ls.

c. Is there any better way to have a form for this kind of referral programs?

Performing community search didn't help me much... If you know other threads similar to this, please link it here.

Your help is always appreciated!