Open-source core with proprietary modules: contribution agreements and license choic

[Nora29]

I'm the lead developer for a small startup, and we're preparing to open-source the core engine of our software under a permissive license to build a community and encourage adoption, but we plan to keep certain advanced modules and our cloud management platform proprietary. I'm diving into the nuances of open source licensing to ensure our business model is protected, specifically around the risks of "copyleft" contamination if someone modifies our open-source core and links it to our proprietary code. For other founders or legal-minded developers who have navigated this dual-licensing model, what are the critical pitfalls in drafting the contribution agreements and choosing the right permissive license (like Apache 2.0 vs MIT) to prevent a competitor from simply taking our open-source work, packaging it, and undercutting our paid services?