I use Postgres 7.1.3 on our development and production servers. We use it because OpenACS 4.x requires PG 7.1.x. Aolserver 3.3.1+ad13 is the aolserver you would want to use. Although I think some people are already running 3.4 or higher with ACS. You may also use OpenACS 4.x rather than 3.2.x its already pretty stable we already have a couple of production sites using it. Use qmail over sendmail the latest version from DJB at http://cr.yp.to is very stable since DJB always gives out very stable and secure software. We also use DJB's daemontools so have a look at it too.
I hope this helps just post on the forum if you have further questions