Please advise how own use sales transactions will be handled while in the sales module and how the own use invoice will be expensed
You wouldn’t use the Sales Module for own use, you would use a Journal. If the own use is an Inventory item then in the Journal you would credit - Inventory on Hand - (Inventory Item name) and the Debit would go to the Drawings account for a sole trader or partnership and Shareholders Loan Account for a Company.
The value would be the Average Cost figure for the Inventory Item