See Mobhack->Help->Weapons Tab->Weapons Class->class 19 info box
Also check the differences between class 4 (flak), 5 (C/BMG), and 19 (e.g. what happens to suppressed class 4 weapons class vis a vis autocannon class 19..). Check what it says in regard to class 19's AAA (or try flying some helos by an autocannon equipped APC company by nature of an experiment
)
Also recall that fire control and R/F costs extra points, once you run the unit through the cost calculator.
As to which and what should have this or that - well how long is a piece of string?. In other words, it is up to the OOB designer, especially if there are no recommendations in the Mobhack help "
Design information,standards and guidelines for OOB database designers" section. Checking other OOBs and see what the designers have done there for similar stuff in the same era, is also another idea.
Andy