I just measured my completed Bruh box with a pair of digital calipers (Yay, first excuse to use it!!) and I measured it on end - meaning the end where the PIR sensor would be sticking out
It’s roughly 35mm wide by 40mm high by 60mm deep so that should give you something to go on.
The smallest box in the image you linked to should fit it, but cutting through ABS could be a bit of a challenge. If you’re not going to use the thermal sensor you won’t have to do any cutting outside of the holes for the PIR and light sensor and a notch for the plug.
It’s a matter of personal taste I guess, I need the temp and humidity, especially in my office where I print. PLA - which is the filament I use to print the boxes with - is affected by humidity and temperature. I also have an enclosed porch that is not heated/cooled. It’s setup like a Japanese tearoom and serves as a great place to read or chill and watch TV. I like to keep an eye on the conditions in there.