Madhur,
1) Correct, if you are doing COLD start then any changes made on the THRESH command display will need hardened in CNM4BPRM(MVSTHRSH) to keep them in effect the next time SYSVIEW is started. In any case, your changes made on THRESH will be saved to CNM4BDAT when SYSVIEW is stopped. If you then do a WARM start it will read from CNM4BDAT.
2) Reference this doc about having an email sent when a threshold is triggered:
https://techdocs.broadcom.com/us/en/ca-mainframe-software/performance-and-storage/ca-sysview-performance-management/16-0/scenarios-how-to-articles-videos-and-online-help-topics/online-help-topics/ca-sysview-base-product/email-notifications-on-exceptions-or-thresholds.html