Regarding point #2,
To activate event monitor issue the following command,
SET EVENT MONITOR <<event monitor name>> STATE 0 / 1;
0 - Specified Event Monitor should be de-activated.
1 - Specified Event Monitor should be activated.
If you want to de-activate event monitors you can but if AUTOSTART is
enabled, then every time when the database started event monitor will
start again.
With Regards
Balakrishnan Ethiraju