I'm intending to install Debian and I was thinking if I can install it
from a "testing" CD image (available at
http://cdimage.debian.org/pub/weekly/i386/ )

If so, what images would I need? Only CD1?

If installing "stable" and upgrading to "testing" afterwards is a
better choice, please tell me how it can be done.

Thanks a lot and sorry if this has been asked before,