Using my own server software without loosing functionality?

I've been happily using 'regular' Mac OS X as a server for some time, but I need to replace the hardware I have deployed and I chose a Mac mini server - so now I'm looking at using Mac OS X Server for the first time.

Apple doesn't update the server software as regularly as I'd like to, so I'm thinking that I want to run my own versions of postfix, dovecot, postgresql, and apache (along with my own greylist solution and clamav).

It's not a big deal for me to set it up, but I would like the added functionality of the Apple solutions wherever possible. Has anyone out there used Apple's push notification dovecot plugin and associated service with their own version of dovecot? Can I set up the wiki server and use my own apache with it easily? Can I point anything that needs a db to my version of postgresql instead of the apple-supplied one? Is there something else I'm missing?

I'm sure I can figure this out on my own (eventually), but if someone else has already done some or all of it, I'm happy to learn from someone else's experience.

Thanks in advance!