Testing Zoho Subscriptions

Testing Zoho Subscriptions

I am comparing ZOHO with Chargebee and CheddarGetter to determine which subscription payment system to use for a commercial web site. I have found that there are a few thing about ZOHO I don't understand (questions below). Can you help?

1) We have a web site with thousands of users with existing unique usernames. We would like to use our existing usernames as the identifier for customers on ZOHO subscriptions. But it looks like customer_id's are generated by your server and cannot be set with our own values. What is the process for integrating a web site with existing usernames? For example, let's say I have username "Fred123" and I want to set up a matching customer on ZOHO. How is this done?

2) We want to access ZOHO via the api and hosted pages. If the hosted New Subscription page is called, how is the resulting customer_id and subscription_id returned to my web site after re-direct?

3) How do I delete the testing subscription/customer data?