Update or refresh nnimap buffer in summary mode

[Rohan Nicholls <rohan.nicholls@nospam.myrealbox.com>]

Hello, 

I have just started using gnus, and am enjoying it, however I am still
working out some kinks, and so far have not figured out how to do a
couple of things that would make my life a lot easier, and any help with
this would be much appreciated.  I have done some searching but haven't
found anything yet.

* Can I refresh the summary buffer while in it?  At the moment I have to
  q out of the buffer, and in the groups buffer use "M-g" on it's line
  to get it to show any new mail.  I would be nice to be able to do this
  while reading other emails in the summary buffer.

* Can I automatically have gnus download new messages from the various
  imap accounts after a certain time period?

* I have these set, but still find my mail marked expire is hanging
  around. (setq nnmail-expiry-wait "immediate") I am guessing this is
  the wrong variable, but I can find nothing under the nnimap variables
  that might be equivalent.  I have this in the account settings:
  (nnimap-expunge-on-close "always")
  It used to be
  (nnimap-expunge-on-close always)
  but that was making no difference, so I thought I would give this a
  spin.

I have other questions, but have not yet managed to read the info files
for those sections yet.

Thanks in advance.

rohan