Default sales invoice with first sales order line prepopulated

At our Community Garden all members have to pay a general membership fee. I have this set up as an inventory item but would like to know if we could set up a sales invoice template that will automatically prepopulate the first sales order line with this inventory item? Also is it possible to generate these on bulk?

See my response to your related question for more information. But first, memberships should not be inventory items, but non-inventory items. Inventory is only for material goods you can count.

No, you cannot set up a sales invoice template. But recurring sales invoices are even better because you will not have to re-enter the customer.