Not that easy to answer without knowing anything about the current resource usage.
In case the 3GHz is a hard requirement your options regarding CPUs is limited anyway. For the remaining hardware, make sure that it's supported (e.g. the RAID controller, ...), and sufficient (for RDS you should calculate virtual RAM = physical RAM).
Regarding the licensing, it depends on your needs. In case that you want to be able to run VM based backups, you need to have a paid license. With a single host, an Essentials Kit should do.
André