Be careful - currently available Sansa Clip Jam and Sansa Clip Sport are not supported by Rockbox firmware. Supported versions are Sansa Clip+ and Sansa Clip Zip (and some even older models).
Killer feature of Rockbox for me is possibility to change playback speed while maintaining original pitch. As most audiobooks and podcasts I prefer to listen on 120-130% speed.
More learning is necessary in areas which are more prone to changes.
Hardware architecture and hardware itself are the least changing parts related to software engineering. And as the result OS kernel level development and system programming don't require to relearn that often.
1) I try to spend less time focusing on short distance. Replacing reading with audiobooks when possible was significant for me.
2) I try to notice the strain in eye muscles. As soon as I notice it I tend to relax and this seem to help.
3) I try to reduce load on eye muscles when possible. Like read less from small screen devices or use bigger font size when this doesn't affect usability.
I use Sansa Clip Zip with Rockbox daily and mostly for audiobooks.
My favorite feature is possibility to increase playback speed while keeping pitch intact
In my experience sleeping with lights on causes more shallow sleep.
I confirm it is easier to wake up, but after several days in a row I felt more tired than usually.
I found that blocking all sources of light during sleep and using light to make it easier to wake up works best for me.