Well I use linux and I'm not sure if that's what you're after but there is a yellow icon representing a scroll at the top right of the viewer's window next to the find next - find prev vertical arrows. When you mouse over it says "Switch to scroll mode… etc." You click this and it should switch to scroll mode.
Calibre (free, open source) can convert between various formats, including mobi to epub.
Also, there are third party tools to enable Calibre to remove DRM, if that is needed.
Calibre does not provide any compression tools, but indeed one could use third party tools to compress files in the directory structure. The predominant files to target would be DJVU and PDF files. Using ImageMagick's convert utility, it is not difficult to do programmatic compression (write a script that recursively goes through the library directory ...