You can choose between 2-CPU or 4-CPU license, if you I/O wait is higher than 10%, go with the 4-CPU license. You can upgrade to 4-CPU license later if need.
The trial license is a full 2-CPU license for 15 days.
I have a Dual core Xeon server,using 1 core cpu license of litespeed, holding 1350 low traffic domains. It work great with 1 cpu license.
The server load is always under 1 around all the day.