I have found that the documentation for debootstrap/vmdebootstrap is not very good, and my initial attempt at applying marlas' recipe to a debootstrap version failed. It is very hard to find out where and why.
So, with so much information missing, I think it may be better to go backwards, starting from lxde-Debian live. Also running Knoppix with persistent store under kvm in Debian 8.3 seems to be unsafe at any speed, under Debian 7.6 it is much safer. Lots of bugs around...