Facebook sign up form

Hello, I need some sort of sign-up form for my Facebook page. It is for House of Bubblegum we sell home & garden products on Amazon. I have over 700 followers and before getting more followers I would some sort of sign up form designed to capture customer emails. Obviously Amazon doesn’t let you get customers emails so if you have experience of this sort of thing? Advice on getting people to sign up would be good? Give coupons etc?