checkout process with or without login

-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7
-- PHP version -- : 5.6

Hi,
I'm making an online webshop and I want the purchase process to be as easy at possible.
We've provided FB oauth, user can easily login, but my requirement is that user can decide if they want to login or not and they can still fill out the address form and complete the check process.
Is there a way to set this up?
I would very much appreciate some help with this.

Best regards

Hi, Jerome,
I've checked to registration to be guest, but there are tow new issues.
1. When checking out, it asked for email in another page, can it be in the same page?
2. The same email address could not check out the 2ed time, it will alert: Email address already used

Can this be solved?

Best regards
Scott