yeah i firmly believe getting all 41 hellionaires with grace is entirely impossible. if someone managed to do it that would be mind boggling.
anyway. as for the programs i use: im just using Unity with the Probuilder plugin. that has some disadvantagous but it works with my process, for now. i have used trenchbroom in the past, though, when i dabbled with godot, and it was a great tool. very fun and easy to use. most devs i know use blender, fwiw, and generally try to talk me into doing so instead of probuilder, lol.
i dont plan much ahead of time which actually is becoming a bit of a problem for my workflow, but for the level shown in the demo i think it worked out great. i kinda just keep adding chunks to the map, and shortcuts to loop them back into the rest, until it all works out. idk how to explain it any better than that really