MV_Root.7z isn't a retail Freespace 2 file. If I recall it correctly, it's the archive carrying the root package for MediaVPs. FSO will run just fine without it, but it won't have the graphical goodies provided by MediaVPs.
Yes, you need to have Freespace 2 installed to install Freespace Open. Or, if you bought FS2 on GoG, just the installer file, Knossos can extract everything it needs from it to set up FSO.