Checkout ERPNext (https://GitHub.com/frappe/erpnext). It is based on a metadata framework (Frappe) that lets you build by configuration, so complexity can be handled much better.

Frappe also lets you build extensions (apps), add hooks to standard events, has a built in RESTAPI and more. Here is a quick overview https://www.slideshare.net/mobile/rushabh_mehta/frapp-framew...

Disclaimer: see my bio