Hi @alexfalappa!
If you are aiming to develop a plug-in or tool for AEM, it makes sense to have an AEM instance available for testing and quality assurance. If you or your company are a registered Adobe partner or customer, you might want to reach out to your Adobe representative to discuss the matter. In AEM CS, there is the concept of Rapid Development Environments that might be suitable for the purpose (but you'll need a license for AEM CS).
If you are not yet a business partner of Adobe, you might actually need to purchase a license for AEM CS as there is no public free-of-charge tier for this SaaS offering available from Adobe. As an alternative, you might evaluate becoming an Adobe partner but I don't have details about the process or benefits involved.
With regards to required steps to ensure your plugin is installable on AEM CS, please refer to the AEM CS Development Guidelines. Your code will also need to respect all restrictions and guidelines that are in place for AEM CS as well as passing all relevant quality gates of the Cloud Manager pipelines.
Hope this helps!
