About Blockchain

I think you should start from understanding what Blockchain is, and what it is not. You can start from here, however, there are plenty of interesting and up to date materials around: https://medium.com/loom-network/understa...5f46fe8419

In short: the only use-case that makes sense to address with blockchain in your application is "Byzantine Generals Problem". As soon as you have it in your project, you can use blockchain to build Byzantine fault tolerant system. Read more here: https://en.wikipedia.org/wiki/Byzantine_fault

If you have typical accounting software you do not need blockchain. Thousand of large enterprises use very complex invoicing systems without any blockchain. They are succesfull in their business and their records pass audits. Blockchain won't make them more efficient (but the opposite is true - adding blockchain makes any project more complex, slow and expensive). Moreover, "private blockchain" makes absolute no sense, as it would be nearly impossible to keep it decentralized and independent.

However, I can think of several use-cases when Blockchain might be applicable for invoicing. For example, to timestamp invoice and make it immutable after it was issued to the recipient. In this case invoice is created in conventional transactional database, where it is editable until issuer decided to send it out to recepient. Upon sending, invoice fingerprint is calculated and stored in blockchain with exact timestamp when invoice was locked and sent out. Recepient receives the invoice and calculates fingerprint to verify that it matches with one saved earlier in blockchain. In this case recipient knows when invoice was issued, and that invoice was not changed in between.

EVen this use-case is silly, because in fact there are much easier ways to protect invoice from changing: it is called digital signature and does not require blockchain. Reason for that is trust: tehre is no "Byzantine Generals Problem" when parties exchange invoices, because they typically trust each other, or have plenty of other ways to verify content on the invoice.