1) How to Connect Zoho Desk Support Page with Website?

2) Can a customer get only access to Zoho support Desk only when he clicks on "sign in" button on website? Because I don't want the customer to go directly into the Zoho desk support and raise ticket on regular basis and that would create chaos.

3)When a person login on a website can we fetch that data on Zoho desk?
4) How many agents we can add and assign to a customer?