I do understand your concern. Rank Math is free and the current version you have will always remain free.
We do plan on releasing a paid version but that will have additional features. The Free version will always remain free with all the features you see in the plugin right now.
1). At the moment, rich snippets are part of the core plugin but we are planning on introducing an independent rich snippet plugin that you can use with any orther SEO plugin.
2). The plugin makes use of JSON-LD.
3). These schema types are available in the plugin and you can enable them globally for each of your post types by heading over to Rank Math > Titles and Meta tab.
4). Rank Math already comes with an option to include images in your sitemap which makes it possible for Google to crawl image content that is assigned to your posts/pages/etc. You can find this option by navigating to Rank Math > Sitemap Settings > General as shown below:
Hope that helps and please do not hesitate to let us know if you need our assistance with anything else.