1) udevd works strange, in particular, /dev/ptmx gets incorrect permissions and so xterm, gnome-terminal, etc doesn't work. Solved it whith "chmod 666 /dev/ptmx" in rc.local
2) su doesn't work for usual user: asks a password, and when the password is correct, it returns immediately with "incorrect password", when the password is wrong, it returns the same after timeout. Decided to use sudo.
Vnc worked without surprises: just created necessary entries in /etc/sysconfig/vncservers:
I had to replace ~/.vnc/xstartup with the following to run gnome-session on each user login:
while /bin/true; do
Now I have to install some supplementary software (OpenJDK, NetBeans, Oracle SQL Developer) and create template from this settings. After finishing deploying template, I'll have about 20 VMs for students...