Nope, not even close.
I *tolld* you what tables you need:
*ONE* table for *ALL* inventory items (what you called Stock items). One.
Then when you sell items from inventory, you need a customer record (which might be a new customer or an existing one), an order record, and one orderitems record per inventory item (product id) type sold.
And similarly for when you purchase items: You need a vendor records, a purchase (or purchase order) record, and one purchaseitems record per inventory item type purchased.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.