RHEL/CentOS/EL is better supporter as it's the main distro OpenVZ is developed for. However, they started creating "official" packages for Debian again which should also be up-to-date... but personally I prefer CentOS for OpenVZ nodes.
Setting up the new hardware node and installing as ISPConfig V-Server
Why would you do that?
- Creating a vzdump
- Copy the dump to the new server
- restore from dump on new server
You should be able to use vzmigrate which can migrate on the fly over network so you don't have to vzdump, copy manually and restore again. This should already be pretty stable.
I may be wrong, but wouldn't it be the easiest to just replace the IP's of the current server's in ISPConfig DB rather than re-adding your server?
So you would migrate all to new node, have old + new running. Change IPs in ISPConfig DB (so it used the new ones) while pointing DNS records on old ones to the new IPs and lowering TTL so clients get this fast.
That way, the old server will still be online (trying to point visitors to the new server) and all changes made via ISPConfig are done on the new ones. As soon as some time is over and everyone has the IPs of the new server, you can shutdown the old one.
Would be my idea..