A user is working on importing the company's trial balance and wants to know how to enter the opening A/P and A/R balances in Core without having to create all the clients and vendors. Is it possible to put it all under one project and vendor called 'Opening AR/AP'?
Yes, you can create a project and vendor in Core for this purpose. Then enter the opening balances there. Check the Core Help for details. For the A/R balance, you can use the Manual Invoice option of Invoices and for the A/P balance, you can use the Vendor Bills screen.
Alternatively, you can create a new journal entry for the A/R and A/P opening balances in the General Journal screen. Check the Core Help for details.