Few doubs about backing up a server 2008

I just installed CB on my Win Server 2008 R2 home server. It is a real server, hosting SQL server, mail server, FTP server and several web sites.
I have 2 500GB HD inside it, and they are mirrored using Windows option to do this. This means I have just a C: volume which runs on two mirrored HDs.
I now want to make a periodic backup on an external USB HD, and this is the reason of installing CB.
My questions after the first backup are the following:

  1. I made a full disk (image) backup and noticed that, during it, no time to end forecast was showing as well as the progress bar was always at 0% … furthermore the backup lasted a bit more that 8 hours … is this all normal ??

  2. taking in account the time needed to backup an image, is it possible to make differential backup of HD … I mean just was changed compared to the last full backup ?

  3. I noticed that CB made a backup file almost the side of my HD (470GB), which means that it also backued up the free HD space (my HD has around 200 GB free). Notice that I used “low” compression (worrying of delay for higher compression) … isn’t it possible to avoid this and create an image of just the size of what is written (jn my case around 300GB instead of 470 GB) ??

  4. Considering that I have 2 mirrored HD (disk 0 and disk 1) in my server, how should I make my system backup ? Now I made drive backup of disk 1 (one of the two mirrored), is this correct ?? or should I make backup of the dynamic C: volume ??

Thanks for your help.