[Exim] Exim + courier-imap, exim rewrite , message delayed s…

Hi !

I'm currently setting up a mail-server with debian 3.0 stable using

exim 3.35 & mailscanner (+ clamav + f-prot + spamassassin) & courier-imap 1.4.3
using the Maildir format, and doing some rewrite of email-addresses.

So far, i've managed to integrate mailscanner into exim
(splitting exim into two parts, one for incoming and one for outgoing),
setting up exim for using maildir (appendfile transport),
doing some email-address rewriting (found a snipet provided by eximconfig)

but several questions remain:
  1.) Where should the Maildir base of the system be ?
      /var/mail/username/ or /home/username/.Maildir
      or where is the courier imapdaemon looking for it
      or why is the d** imapd not working
  2.) how can i rewrite the addresses only for mail not destinated
      for local users. I found a snipet in the exim-faq,
      and tried to integrate it for me (see below) but its not working
  3.) how can i set up exim to send a message-deliver delayed message
      back to the local user if the message is delayed for more than 1 hour ?
  4.) (Dummy Question) As a localmailserver, can i deliver messages
      without a smarthost or do i violate rfc822 or something similar,
      or, the other way around, when do i have to use smarthosts ?

/// from exim.conf ///
remote_smtp:
  driver = smtp
# Rewrite of email-addresses for external mail based on /etc/email-addresses
  headers_rewrite = *@saturn \
      ${lookup{$1}lsearch{/etc/email-addresses}{$value}fail}
  return_path = ${if match{$return_path}{^([^@]+)@saturn\$}\
      {${lookup{$1}lsearch{/etc/email-addresses}{$value}fail}}fail}
///

Thanks in advance,
Felix.