I'm making an armedbuilding (specifically a static turret with no moving parts) and I need to arrange the firing points, the aimers, the hierarchy, etc.

I've talked to several people but they seem to not entirely know, or they're no clear, or the answers are inconsistent etc.

Where I am at: I have appropriate nulls facing the right direction on the tip of each barrel of the turret. So now I need to know what do with the hierarchy, aimers, and other stuff to get the gun firing.

What is it that doesn't seem to be working for you?
If you say it has no moving parts then you don't really need a hierarchy, just a hp_fire at the end of each barrel and maybe as children of the turret mesh and you're done, just use the turret mesh as the aimer, if it doesn't move then it doesn't matter.
Have a look at:
hoth_bldg_ioncannon.odf
in:
\BF2_ModTools\assets\worlds\HOT\odf