The answer to some of your questions are as follows:
Yes you have to have the OMS to run the OEM and the OMS is the one that maintains the repository on the activities that you set.
You can set an alert even using the OEM event to fire a mail or pager message to you. To this you have to set your SMTP or pager options under the Prefered credentials and send out a test message. Then go ahead and create an event, that would monitor the database and also don't forget to check the notification check box checked (one on the top and on the bottom pannel of the wiz).
Set your notification timings in the prefered credentials and that would awake up and check for the notification. I would suggest turn on the notification for 24Hrs.
Hope that this would help you to roll.
If you have any further questions, pl. let us know. For docs refer [url]http://technet.oracle.com[/url] and do a search on OEM
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