Hello Kevin,
I’m sorry, currently we don’t have any option to turn off Check for Updates. A PR is filed for the dev team, to address this issue. Sorry for the inconvinience caused.
I’m not sure, what you mean by
In addition the Content Assist desire to look at http://www.sun.java.com for javadoc is also throwing you an authentication dialogue.
Can you send me a screen shot and steps to reproduce this?