Hello Philippe,
1. Firstly, please specify if you are going to have a shipping option on your website? If yes, please go to Shipping configuration and turn on the Free shipping option and set the amount from which the free shipping is applicable.
If you are not planning to ship the products, turn on the Pickup option. You should have at least one of the options turned on in order to be able to go through checkout process.
Also, it is important to make sure that the quote widget is inserted within the magic space {paymentgateways}, otherwise, the quote form can work incorrectly.
2. Exactly, the Checkout widget enables the customers to register once and then use their credentials to log in when they return to the site. Please make sure that you have configured the action e-mails to send the login/password to your customers. Please note that they will receive it if they have passed through check-out process till the end.
Kind regards,
Eugenie
SeoToaster Support