Gas Generator how many watts!!!

That's not much headroom. Which is why I suggested 2KW. I would go at least 1500min. Anything on the order of PA/ music is not a stable load, like lights or similar. Sound system loads are all over the place, with very high peaks. More like motor starting loads I would give that a fair amount of headroom
Exactly. Like if you run a air conditioner, you need to know the surge amperage to start the unit. Like you said the light current doesn't vary much but the amplifiers will. Honda's Eu2200 looks like a popular model and should have plenty of power for what the OP needs done.