It's good you're using QuickBooks to manage your vendors and clients. I'd be happy to share info about setting up both a vendor and a client.
At this time, QuickBooks doesn't allow duplicate names. This mean that you won't be able to add both the vendor and client using the same name. A common workaround to this would be using a different name or adding a character such as a period in one of the names. For example, say the client's name is Phil Collins and you'd like to add him as a vendor as well, you'd have to enter Phil's name as Phil. Collins in your vendors list.
Here's how to add a supplier/vendor:
1. Select Expenses, then Suppliers.
2. Select New Supplier.
3. Complete the fields in the Supplier Information window.
4. Select Save.
Here's a helpful video which shows you how to add a customer in QuickBooks:How to add customers to QuickBooks.
In case you have other questions, feel free to contact our support team using this link here.