Great work on the themes. I’m currently working on one that looks similar to yours, although I don’t really know how to make the themes from scratch so it’s just using other themes as a base, haha.
Have you thought about adding 3D box art (http://www.theoldcomputer.com/game-box-art-covers/Nintendo/NES/3D-Boxart/1943%20-%20The%20Battle%20of%20Midway%20%28USA%29.png) and an open box (similar to the screenshots in your second post) for metadata to the space below the snapshot? I actually wouldn’t mind doing that for the theme I’m using, but not sure how to do it.
If you decide to do Sega, here is a pack of Genesis title screens that I made for my set if you would like to use them. There are a bit over 600 snapshots, none of the sizes have been changed, so they’re the default resolution the emulator puts out.
https://www.mediafire.com/?92rel5dz4bc4049