KDE dolphin. I have no idea what you are describing in half your items, but it certainly has preview panels, and lots of things you don’t mention: open terminal here, synchronized terminal panel, split windows, support for browsing over SFTP, keeping folder tree as you browser down or not, zoom, etc.
Probably no one’s thought of this yet, but i’m going to say black electrical tape. If you put it over your eyes it takes care of all your devices at once.
This sounds like a great idea. I would suggest doing also other things that simulate the brain in other ways, like listening to music (or even playing an instrument), visual stimuli (art, nature), physical motion and coordination activities (dance, sports). You may well already do these things, I just felt I should mention it since our culture is so prone to associating brain with mental logic specifically and forgeting how much these other things involve the brain.
Learning a language is another thing with really strong evidence for brain development /preservation.
Also, fuck ZDNet for autoplaying a video on this page.
Gnack is the open source version.