should i even use moderator user? im running an education website with these user groups
Whether you need moderators or not is entirely up to you. Moderators have full permissions to moderator user profiles and their content in addition to the content of nearly all plugins.
error
:: Action 95 :: Condition 1-1 failed for user 1000262 with "Event Manager" Equal To "Students"
That looks like it's working fine. As explained earlier you should have 1 auto action per type so in this case the auto action for "Event Manager" would have worked. So a few of them will fail like that since their conditions are doing as they should. Just be sure to turn off debugging in the auto action once you're done.
from the user management, after registration all users are in the selected group but the userlist didn't reveal any user. i configured the usergroup for each user lists.
Not sure I understand what you mean by this. When configuring a userlist in CB > List Management be sure to select all the usergroups you want it to display in the "Usergroups" parameter. You then of course need to add columns to your userlist. I highly suggest reading the CB Primer Book, which you can download below as it goes through all the basics of CB.
www.joomlapolis.com/downloads/documents