I am installing a new router running on ROS v5.2 and DELL R300 (Multicore=Yes).
I want to test the performance of this router but I am not sure what is the correct way or step to do this test.

Can anyone advise?

Kinda depends on what you're looking for. Throughput in Mbps? Throughout in pps? Number of hotspot users? Number of PPPoE users?

I would like test as below:

1. Throughput per Mbps
2. Number of interface VLAN
3. Number of PPPoE