Given your large number of sites, the other thing you’ll need to check into is SSL certificates. I was also using WHM’s backup to a separate drive, which IW didn’t support via the GUI however, IW Support provided me with a very nice script I run via a cron as root that does the trick flawlessly. One other issue I ran into was that I was using DNSSEC for all my domains, and Interworx did not support it at the time of my migration, so I had to disable it in WHM and at the registrar prior to the going live. Since everyone is moving away from CentOS, it would be nice if they were using something else so that you don’t have to migrate again to get an new OS when that situation is settled. One question I would ask if I were you is what OS Liquid Web will be using for your new server. If you use port 465, you will need to update your mail clients to connect on 587 instead.” That is not true however, it is a good idea to upgrade your mail clients to port 587… For example, it says that “InterWorx’s mail program does not support SMTP on port 465.

Liquid Web does have a document regarding the migration, but there is at least one error due to out-of-date information. There are a few gotchas that you need to be aware of.

I have a dedicated server with Liquid Web, and they migrated my ~30 sites from WHM/cPanel to IW a couple of years ago.

Comodo modsecurity cpanel