Ask HN: ERP system suggestions

We are looking to transition to a new ERP system. We've been running the same software since the 70's, and it has been highly customized over time.

We'd like to invest in a platform that allows us to modify all aspects of the system, while also starting out with a base that doesn't necessitate starting from scratch (i.e. prebuilt accounting, payroll, etc functions). Preferably the system has an open API for extending the system as necessary, and integrating with third party software.

Any suggestions? We are in the metal wholesaling business.