Hi,
Is it possible to add a link to the archive page for each post type at the end of its group?
I’m afraid that’s not possible. I recall someone may have asked this very same question, it might be on the future features list, I am not sure. It is possible it may get added later on as a core feature.
Can I reduce the number of results displayed for each group?
Yes – under the Search Sources -> Limits panel, you can set the number of results for both taxonomy terms and post types: https://i.imgur.com/uHoyuvq.png
If you want somewhat matching number of results for each post type, you can try this option as well, however it may cause some funky number of results in this case, so make sure to test it.
