We are planning to switch to Zoho Subscription but there are some pre-sale questions

We are planning to switch to Zoho Subscription but there are some pre-sale questions

Hello,

we are planning to switch to Zoho Subscriptions but we are not sure if the following things are possible. 

We are currently running an online shop (based on WooCommerce) and are thinking about sending all subscription orders via Webhook to Zoho Subscriptions (i.e. via Zapier or directly from WooCommerce to Zoho Subscriptions if possible).

And we are using a few payment methods/gateways that are not supported with Zoho Subscriptions (i.e. TWINT, Saferpay/Six Worldline and QR-Bills). So we are thinking about synchronizing the payment status via Zapier from WooCommerce to Zoho Subscriptions. 

So here are my questions:
  1. We do have a few thousands of existing subscribers (before we used WooCommerce) who do not have an email address. Would that be a problem when migrating/importing the subscribers and subscriptions to Zoho Subscriptions? 
  2. Can  new subscribers automatically receive an invitation link to the portal?
  3. Do we have to pay extra for the customer portal?
  4. Is it possible to add custom fields to the customers and subscriptions?
  5. If someone wants to buy a gift subscription for someone else is it possible to add a billing address incl. first and last name that is different from the shipping address (also incl. a different first and last name)?
Thanks a lot for your help, 
Michael