Thanks for the feedback. Splitting up the current module is also on my mind. In my opinion, commerce_stock would work just like the simple stock module in D7, which would work out of box with inline_entity_form and only keep track the on-hand stock.
The rest of stuff would be Inventory Control Workbench (screenshot above) and Stock Movement. These two might be nice to fit in a submodule.
On the other hand, I haven't thought about integration with external ERP, as I haven't used any ERP at all.