I started using zoho today and have questions as I set it up for my business.  Any help will greatly be appreciated!!

1. how do i make invoices for vendors?

2. how do I assign a client to a vendor?  We broker deals between vendors and clients

3. how do i add custom fields to a potential?

4. is there a way for me to collect data from my website without having your form on the site?  I already have the order process setup and would like an easy way to integrate zoho.  Maybe a way to collect data from emails?

5. Is there an easy way to distinguish which one of my website a lead came from?  I have about 5 distinct websites, each with unique marketing and i would like to be able divide up customers by the source website.  I would also like to split them up with I send out mass emails

6. What are examples of campaigns? 

7. With google app integration, does zoho automatically track which customers have been emailed and when?