Boundary (http://www.boundary.com/) Never needed to use anything else, it has worked perfectly for me... Pretty graphs and Notifications for High CPU or High RAM and outages..
LOL... I would laugh so much when that "technical error" is really a table that just puts everyone into disney characters depending on there ethnicity :lol: and they did not select the right row to get the name from xD
If you are using SolusVM as your VPS CP then take a look at this link its the SolusVM WHMCS Module Guide i gave the direct link to setting up to use different locations.
I have always used CentOS and never really had any issues with it, so I do not really have an opinion on any of the other Unix based Operating systems xD