Initial value in comments box

I would like to add something like:
"Comments are moderated and will not appear immediately" somewhere - maybe as an initial value in the text box or something that appears after they hit "submit".

How can this be done?

Also - Is there a way to activate/create a "Thank you" bar to appear after 'submit?'...give them confirmation that it went through?

Thank you,

Michele

PS. As always, sorry if I missed an obvious solution to this.