The firewall has to be disabled on the host server. You dont need it anyway on the host as only services are installed and listening on external ports that shall be accessible from outside when you followed the installation guides, so enabling the firewall does not have any security benefits.
My problem about quota is that if quota is on on the same disk as openvz is using, ISPConfig cant create new machines.
A server that hosts openvz machines shall not host any websites anyway as the websites are hosted inside the virtual machines and not the host system, so you can disable quota for the whole disk. Please see openvz setup guide for ispconfig and dont use the perfect setup guide (which is for webhosting and not openvz) to install your openvz host.