Thanks to worktroll for doing all the work on this one:
1) See TO p131:
""Advanced buildings may install weapons, heat sinks and
other equipment in accordance with the rules for mounting
weapons and equipment on Mobile Structures (see p. 266),
but with a few modifications as outlined below."
This and subsequent pages address issues involving turrets, power amplifiers, heat sinks, etc - subject to the modifications noted. Summary - unless otherwise stated in TO beginning on p131 or p266, assume buildings default to vehicle rules for these things.
2) The key here is "for any and all Heavy- or Capital-class energy weapons mounted on the" <building>
Heavy and Capital weapons are defined in TO (and many other places) - for an approximation, Heavy are 'mech-grade, Capital are WarShip-grade. So - unless powered by fusion or fission style plants - power amps are required for PPCs, Lasers, Naval PPCs and Lasers, but not for NAC, autocannon, or missiles.
3) See above - TO p131+ and p266+ provide the relevant answer.