Hi Jeff,
question 1: Syslogs are useful to find out why a connection did not get built, why the device rebooted, was there any attack, etc. For troubleshooting an issue, syslogs are very important. So, disable the messages according to your own discretion.
question 2: You can disable some very general syslogs messages like built and teardown connection messages. The command is "no logging message ".
question 3: Enabling or disabling syslogs is completely your call. You can disable the syslog messages you don't need.
Hope this is clear. Here is a document that might help:
http://www.cisco.com/web/about/security/intelligence/identify-incidents-via-syslog.html#9
Hope this helps!
Regards,
Anu
P.S. Please mark this question as answered if it has been resolved. Do rate helpful posts.