At the moment, the software updater is an application you run manually. Later on, it may also provide a notification that updates are available. But that’s it, we don’t plan to sneakily install updates without the user accepting them first.
I don’t remember the exact specs for the Mac Minis. Anyway, if you want to run a build bot, all you need is a machine (real or virtual) running Haiku, online most of the time, and accessible through ssh. It does not have to be similar to the Mac Minis (in fact, none of the package build slaves at the moment is using one of these).