There is no limit, you can refer as many friends as you like.

When your friends click the link you've sent them, the discount is automatically added at checkout. Once they make a purchase, you will get an email with your own discount code.

Yes, you can. You’ll get a new discount code every time a friend makes a purchase.

A referral link is meant for new customers and can only be used once per friend. If the discount code is not applied, they’ve probably ordered before.