Wei-Shang,
I would like to confirm your estimated efforts to setup an SAP environment.
Honestly - it takes me a bit more time with all the preparation, checking and implementing OSS notes and post-processing.
Yes - during the project lifetime I have a dedicated FTE for SolMan - just to manage SolMan and support the functional consultants.
The benefit for the PM is that everything is proper documented, we have the monitoring, reporting and alerting landscape ready, we use lots of the self services before Go-Live and the transition to BAU runs smoother.
This reduces the risk and _saves_ costs...
cheers
Kay