Love the setting idea, and the piston knight concept! The description reminds me of the gas-powered mobility gear from the anime Attack on Titan, which might actually share some thematic threads with your setting idea.
All the voice games I've run or played in have used a music bot, usually Groovy. It's worked very well! Individual players can adjust the volume to their liking, but I think it's definitely a cool option. YouTube has lots of good music to use, and you van even make playlists that will auto-cycle.
I personally think so, as a lot of the games I'm in are more about treasure and exploring, but in any game I run there's at least one clearly pure evil faction that the whole gang can battle with no moral qualms, sort of like Raiders in the various Fallout games, who cannot be reasoned with and...
I find Farscape/toned-down Guardians of the Galaxy is my default playstyle -- not afraid of slapstick but there will also be some ugly death guaranteed. A slightly more Robin Hood version of Murderhobo.
The character was probably referring to the interrogator squid creature from Rogue One, which is pretty close to being a "mundane" mindflayer.
Edit: Those are apparently known as "mairan"
I don't hate them, but I find them so uninteresting I guess. I'd welcome a Goliath PC but otherwise they wouldn't be a presence in my game settings - I'd likely just use really tough humans or Earth Genasi.