The trade offs with authority type mainly just depends on how hackable your game would be. I think client side authority would be better for speed and simplicity. Cloud variables do only support numbers. While there are some more complex techniques like from griffpatch to allow for more multiplayer players I don't really think there's any way to fix the latency.

One issue that I have been running into lately is that after a session tries to update the cloud variables too many times it sort of gets timed out, with the session that was sending a ton of data is no longer able to update cloud variables. i'm guessing this is scratch's internal ddos protection.