RE Lightening quick
can't be done. electricity moves much slower than lightening.
RE PC & PLC
the supply cable to the PLC adds its influence to everything downstream of it. naturally then this single PC can be quite influential and one can deal with it either right off or later on with this knowledge in mind.
RE power on 24/7
its all about heat. well, almost.
with consumables like tubes, especially NOS tubes, judicious use is pretty much preordained. shut it/them down when not in use, unless you are sitting on a goodly supply of vintage tubes.
... or you don't mind re-tubing more frequently.
if you can control the temps where the gear resides and maintain it pretty chilly, I'd say leave whatever on all the time.
if the gear is pure Class A it has to be running a signal which will lower the temp and or increase the efficiency of the amp. even if the volume is very low.
heat, especially excessive heat kills electronics more than repeated powering up and down.
in the Navy shipwide public address system was all tube based of course there were other sensitive electronics which when energized were kept on for months at a time without failures due to heat because the ambient temp in that space was maintained quite low..
certainly it was quite cool in that space! ambient temps were usually in the low to mid 60s.
lessen the ambient temp, keep the gear cooler and you will extend the life of your electronics.