Sorry if this has been covered before but I have 2 questions -
1. Is it possible to add custom fields to the welcome email?
2. Is it possible to create multiple welcome emails based on different subscribe forms?
Yes it's possible to add custom fields to the subscriber confirmation email. You can't create entirely different welcome emails based on the different subscribe forms, but you could use the custom fields (possibly as hidden fields if needed) to make the different forms pass along unique information to the confirmation email.