I have some questions about making Qemu disk image.

1. In QEMU_Build_Tutorial ,one step is to copy root file system to the diskimg " # cp -R /* /mnt/rootfs ",I what  know what files are necessary ?(I don't want put all of it,it might be too large) 

2. Is it necessary to put Debian in diskimg?

3. I can't figure out this situation :  

I can't successfully boot my disk image ,but can boot by QEMU download image,so I try to create a empty disk image , format it as (EXT2/EXT3/EXT4). mount QEMU download image and copy all of files into my image mount's directory.Boot my disk image again,and It does't work.What's wrong with my idea?I thought change my image contents to download's and it can be work.It seems not.

thank for your help~