Shanmuga,
Start/stop order?
1: If the DB is being stopped stop the DA, then stop the DB.
2: PC can be stopped/started first or last but if stopping the DA and DB as well, we'd recommend stopping it first, and starting it last.
3: DCs should be stopped as little as possible to avoid data gaps. Only stop them if necessary and restart them quickly to minimized missed polls and data gaps.
DB start/stop without password?
Stopping and starting the DB without a password is not an available option. It is required and any change to that would require an Enhancement Request to request the change to the functionality. Submit one if you like as an Idea post here in the Community forum.
I'd recommend opening a new case with support for your Data Aggregator restart problems.
Thanks,
Mike