If you have customer contact data that also acts as a supplier in your store, you can directly assign the customer contact data to supplier contact without the need to create a new supplier contact manually. To assign the customer contact to be a supplier, you can follow the steps below:
Step 1. Go to Contact (Customers Tab), then Select Any Customer
Click on one of the customer names that you want to make as a supplier too.
Step 2. Click the Arrow Button, then Choose Create Supplier from this Customer
Click the Down Arrow Button on the Contact Details Page, Then Click "Create Supplier from This Customer".
Step 3. Supplier was Created from Customer Contact
You can try to make sure the supplier data in the contact menu:
To add a new salesperson, you can check this article Add New Sales Person
If you want to create a customer group for multiple customers, you can check this article Create Customer Group
If you want to add customers/suppliers in bulk, maybe you can check the steps in this article Import Customer / Supplier
To add a member exclusive for an outlet, you can also check this article Member Exclusive for Outlet