Great work. Everything you say in your Readme about existing systems is true.

I notice you don't have financials yet. In my opinion the API approach is really difficult to get right with financials. Every finance professional will tell you nightmares about 'the stock doesn't balance between the two systems'. The first reason on stock is a costing problem, you must have the same costs in both systems, so every purchase cost change, every bom roll up must change both. The second is on quantities. This is usually caused by a stock movement that somehow failed in the API to the financials. If it is done in a more tightly coupled way, you post the stock movement and the financial movement inside a database transaction and it either fails everywhere or posts everywhere. I worked on one system where it posted each half of the double entry in different transactions, so would fail and leave the ledger out of balance! Happy to chat further