How much "CRM" is relevant to single pilot ops?
What is really important to SP ops is good cockpit organisation. For example sort out the approach plates 0.5-1hr before arrival, etc.
CRM is very relevant to single pilot operations. Cockpit organization is certainly a part of it.
CRM was a buzzword for some time. Others have taken it's place, but the concept is still very valid.
CRM is sometimes thought to be crew resource management, but it is originally cockpit resource management. That covers every aspect of the flight; CRM is learning to better manage the flight.