It feels a bit hacky.
Mostly because I would be needlessly double-checking the figures and items match, if I need to make any changes (which I shouldn't, if an invoice is issued. But such is life).
There's redundant selections like "paid", if not wanting to leave it as draft.
I cannot use the same number as the invoice.
It would also be much nicer to have additional invoice properties like "paid on" and "receipt issued", which would help my bookkeeping a lot. A receipt feature could involve these.
Lastly, I feel (semi) duplicate items under the invoices directory is visually fatiguing.
I'll give the duplicate idea a go in the meantime. I'm aware that my above thoughts are no small ask, so thanks for the reply and thoughts Timo.