RE: sales and purchase without vendor no and customer number
If you do cash sales and cash purchase you can register that in a general journal by posting credit your sales account and debit your cash account.
But often local regulations will require you to produce an invoice or a cash receipt so most regions can not use that methode.
You can also create one customer and and vendor that you use for all transactions. Nothing I would recommend, but it is doable.
Like a common customer and a common vendor.
