Merge New Cisco MDS 9148S (ISL-PortChannel)

Hi

could you help me please?

i am going to config (merge) 4 new switches cisco MDS 9148s in pairs by using ISL-Port Channel (cascade)   sw1-sw2 and sw3-sw4, but a am not sure how to set the static domain id, i mean (when: before or after the ISL and port channel config), where (just one sw or both switches, how (set the domain ids) and what commands do i need to use to do that?

Best Regards