You'll probably need a script.
But do you have this setup for your tables for the invoicing part of the process?
Customers----<Invoices-----<LineItems>-------Products----<KitProducts ----< means "one to many" and KitProducts is a second occurrence of Products
And do you intend to list each of the items that make up the kit as individual lineItems records? (The main place to use a script is to determine whan a selected Item is the ID for a kit and then add the additional line items records using the quantity specified in combination with info from KitProducts.)
Once that works for you, LineItems can actually be an occurrence of a "transactions" table where each record created documents an inventory change for a specfic item in Products.