Gradual move to own mail server - strategy for noob

[Barnaby Scott]

Hi, I'm trying to replace my current arrangement for email, and though I 
have read as much as possible on it, I just want to check if I am on the 
right lines with what I'm planning. (Is that a legitimate use of this 
list?) It's the same old story, when you're a beginner it is very hard 
to take even small steps until you have a grasp of the 'big picture', 
and know what direction you should be going. So I'd be glad of any 
opinions, pointers, or How-Tos that I may not have spotted.

If you read the rest of this, you may think that I'm trying to implement 
something way too heavyweight for what I need at the moment, and you'd 
be right! However, I want to learn, and enjoy trying to master the big 
boys' toys.

OK, so here's where I am:
8 users
3 or 4 Windows machines including a laptop - users may use any/all of these
New FreeBSD server so far only operating as a Samba server (PDC).
Email is downloaded by individual clients from ISP via POP3 - user must 
be at specific machine to access their local mail folders. If elsewhere, 
they must use webmail, but of course sent messages, replied flags etc 
are then inconsistent, besides which messages are only left on the (ISP) 
server for a limited time.

Here is where I want to get to:
IMAP server on my FreeBSD box (and using Maildir is my instinctive 
preference.)
Ultimately, but not yet, I want to start using the FreeBSD machine as a 
proper mailserver - i.e. get a static IP address and point the MX record 
hosted by my provider at it. For now though I am happy to fetch from the 
existing mailboxes that they host for me.
Again, not necessarily now, but when I am fully up and running, run spam 
and virus checking (that's done for me now, but inevitably could be 
improved on.)

What I _think_ I want to do is this:
Install Fetchmail to get mail from my various hosted mailboxes
Configure Sendmail, which I accepted as the default mailer
Install Procmail to deliver messages in Maildir format (to users' home 
directories?)
Install Courier IMAP as the IMAP server

Ultimately, then drop Fetchmail and reconfigure Sendmail for receiving 
mail directly, and add anti- spam and virus tools.

Have I got this about right? Do I really need 4 separate tools to do 
this? Have I overlooked something more obvious/elegant? Where are my big 
pitfalls going to be?

If replying, please keep in mind my embarrassing level of inexperience!!

Thanks

Barnaby Scott