new old ereader - PocketBook 622

Hello,
I recently got my hands on a PocketBook 622. I really like it, but I have a few questions about it.

1. How can I change the order of the icons on the main screen? (Books, Dictionary, Settings, etc.)
2. Can I install any additional apps on it? I know that modern e-readers usually have lots of different apps available like KOreader.
3. Is there a dark mode?
4. Do you recommend some fonts that help with readability, it doesn't have high dpi so the text is a little blurry. I like serif fonts.
5. Do you recommend anything else? Like some must have settings or must have things to do to it.

Thanks in advance!