Best platform for a self-hosted internal Sales Hub?

I am evaluating platforms for a mid-sized distribution company. The first project is a Sales Hub where staff can search a product once and get pricing, inventory, sales history and availability from our internal SQL/ERP system plus multiple external vendor APIs/web services, instead of checking 10–20 different websites. Requirements are self-hosting initially, cloud option later, SSO, SQL/API integrations, good security and the ability to expand into a larger platform. Currently considering Retool, Mendix, OutSystems and Appsmith. Has anyone built something similar? Which platform would you recommend based on real-world experience, scalability, maintainability and vendor lock-in?