In general, if you're not sure about something with V9, don't do it. Don't try if you're not comfortable "flying blind" or having to recover if it doesn't work.
That said, here are some quick answers:
> Would it be a good way to back up the music files to just copy "C:\Music" to a CD or other area? then import "C"/Music" to the new player Version 9?
Copying your music anywhere would be a good idea, but it may take some time.
An alternative is to make a new folder with a few albums in it, just to experiment. \music2, for example.
> If uninstalling MJ8 will it also delete the files in "C:/Music" ?
No, but don't uninstall. Just install 9. Remove your old database files (it's in the instructions in the thread announcing the preview).
> The right click " statistics " in Media Library in MJ8 say: Files = 2055; Artists 486; Albums 135 and size 6.041Gb WHILE the right click "Properties" in "c:/Music" say files 1882; folders 243 ; and size 5.91Gb. Shouldn't the folder number (243?) be equal to the number of Artists(486) ? note: I noticed this while trying to import into Windows Media Player and couldn't find all of the artists? Even after "update library" including "Update all database fields:
Maybe some music is in other folders.