i have a similar config 3 esxi, freenas as iscsi san-nas, my vcenter run with 2vcpu and 4 go, ad 1 vcpu is enough even with 40 vm. i have also vshield installed, trend micro deep security 9, vcops and view... looking for vcould director in next weeks... I have also few plugin like eaton ipm for vcenter netapp...
always try to add more memory before vcpu...