One login for all site members

Hi,

Well, you can have several persons use the same credentials to access the same user account. It's just that the email notifications will go to one email address, the one of the account, etc.
If you want the shop to be accessible to them only, then just have a user group for that user and limit the products/categories/menu items to that user group. Others won't see them.
If you want to remove the address view from the checkout, you can configure the "checkout workflow" setting:
www.hikashop.com/support/documentation/2...eckout-workflow.html
And if you want to add a membership number field, you can create a custom field of the table "order" via the menu Display>Custom fields.