Hi!

I faced with several difficulties / misunderstandings and I hope someone could clarify me (at the moment I use 'virsh' for testing).

1) after creating network via 'virsh # net-create network.xml' i get vzbr0 bridge in down state and have to make ip up manually. Is there any way to automatically make it up?

You can specify an IP address and a netmask like this:
http://libvirt.org/formatnetwork.html#elementsAddress
Such bridge will be automatically set up.

2) there is a default network "Default" with enabled 'Autostart'. Is there any way to remove this network completely?
Yes,
# virsh net-destroy defaul

correct answer is
# virsh net-undefine default

3) after creating domain via 'virsh # create ovz.xml' i get a new container, but it doesn't work as it should do:
- at first, it has 'vzbr0' veth interface inside and its pair on a HW node is added into default bridge vmbr0. I believed tag <source bridge='vzbr0'/> should point to a bridge name on a HW node, but instead it created veth interface with such name. In openvz config file for created domain i see this:

[root@alt-03 ~]# cat /etc/vz/conf/3005.conf | grep NETIF
NETIF="ifname=vzbr0,mac=52:54:00:35:10:6D,host_ifname=veth3005.0,host_mac=52:54:00:35:10:6D"
Short answer: it doesn't work now. Wait for nex libvirt release (libvirt-4.6-alt2). I will try to make it as soon as possible.
For details see
http://www.redhat.com/archives/libvir-list/2008-October/msg00323.html

4) Is there any way to specify config file for created domain like it can be done via 'vzctl create <ID> --oostemplate <templname> --config <confname>'?

No

5) Is there any way to destroy domain completely like it can be done via 'vzctl destroy <ID>'?

Yes,
# virsh destroy <domain-name>

And here too, if domain was previously defined, command must be:
# virsh undefine <domain-name>

6) Where does libvirt store info about already created domains? I can't create a new domain with ID 3005 after I completely destroy previous one via 'vzctl destroy 3005'.

And what does it saying?

7) Is there any way to publish domain's console on a host system so that I can connect via telnet to HW node on some TCP/4567 and get into domain's console?
vzctl enter <domain ID>

8) Does libvirt use some OpenVZ bindings or simply executes vzctl and other stuff?
simply executes vzctl and reading/writing <veid>.conf

P.S. You can ask ALT-specific questions to me directly.