Hi,
There are numerous softwares you can install, the main 3 that is good for reselling on WHMCS/Blesta, are:
1 ) SolusVM
2 ) Virtualizor
3 ) Proxmox.
Virtualizor is the easiest to set up, has a simple UI, for single servers, its the best, but please note, if you google reviews, or virtualizor problems, you will notice, across many servers/ after creating and destroying many nodes, it eventually runs to a HUGE amount of problems
SolusVM is like an old old software. It works, but it uses an old code, so its difficult to set up, but once its done, its pretty stable and works fine
Proxmox is new, but u need a lot of coding knowledge/experience to get it working fine. It also works best across clusters of servers.
JUST AN EXTRA MENTION : NEVER TRY RUNNING TWO TYPES OF KERNELS ON THE SAME BOX. I KNOW VIRTUALIZOR LETS U RUN OPENVZ AND KVM on a same box, but dont do that, unless you're ready for a lot of work
