Exchange from behind a proxy server

I have several questions I will ask in one.
1) I want to put up an exchange server on the public side of my proxy server. Will my private network clients be able to connect to Exhanges’ collaborative folders (i.e. ‘All Public Folders’ folder)?
2) How will I logon to my NT domain from the public side of the firewall?
3) How will private-side clients connect to my exchange server?
4) How do I set up my Linux Firewall to forward all those requests from both my clients and my server?

Any andall help will be appreciated.