2.)  how to add the wiki under the Add New see the pic for what i mean..

Note: 

The current one 'Job" is from the links plugin, Wiki doesn't add an option for that there

3.) I also noticed that when i remove/delete a post it takes to blank page too.

4.) when members or i post something it shows the error below.

Error 500
Internal Server Error.

5.) I don't want members to have ability to delete and edit categories

Can it be editable for admins only?

6.) I don't want members to edit my posts. 

I think anyone can edit others posts posted by members in userswiki or am i wrong?

What i am trying to have using the Userwiki is something

 that helps people find new temporary jobs and post  Jobs vacancies!