This article may help you: https://support.f5.com/csp/article/K15930
RAM allocation
When you create a guest, the guest will provision RAM based on the number of cores you are assigning to the guest.
RAM per core is calculated based on the following:
(total blade memory - management overhead (normally 4-8 GB))/ of cores = RAM per allocated core.
If you need more RAM for the guest, you must add more cores.
CPU
Because the amount of CPU and memory in a single-core guest is limited,F5 Networks highly recommends that you provision only the BIG-IP® Local Traffic Manager™ (LTM®) module within a single-core guest, and no other modules.
So you will at least need two CPUs per vCMP guests to run 2 modules or more. Depending on the load you are expecting to go through the box and the number of modules you provision you can add more CPUs. Adding CPUs will automaticaly add more memory. Keep in mind you need to add CPUs in pairs of 2.