SQL server Service Accounts permission I will be changing the existing SQL Server Service accounts from the default to Domain accounts from the SSCM which i believe will set all the required permission. One thing I am not sure whether the service account needs to be added as database logins and if so what are the minimum permission needed.
If you're changing the SQL Server Agent Service, make sure you observe this orientation about SQL Server Role Membership from the doc:


  The account that the SQL Server Agent service runs as must be a member
  of the following SQL Server roles:
  
  
  The account must be a member of the sysadmin fixed server role.
  To use multiserver job processing, the account must be a member of    the msdb database role TargetServersRole on the master server.
  


Also, the Configure Windows Service Accounts and Permissions doc should give you information about each SQL Server Service.



You already mentioned you're going to use SSCM to do the change, but since it could be useful to others, I believe it's worth mentioning that it's recommended to use the SQL Server Configuration Manager to Change the Service Startup Account instead of services.msc. Pinal Dave's article explain a few reasons for Why to Use SQL Server Configuration Manager Over Services applet (services.msc)?