For welcome messages you could edit the PM message for new users in the language files from the control panel.
Search for WEL_MSG.
This is the stock private message sent to net new members.
For email you could do the same thing through the language files for new registrations or in the member management area of the control panel you have the ability to send a email to anyone you search for such as new members.
As far as polls go the best advise is to just try it and delete it. Once you vote even as a admin you can't go back and vote again.
