"A bit too much" additionally states, that there is slightly too much / a little bit too much. So what ever it is, it is still too much but only slightly. I feel like you can add "a bit" quite often to make a sentence sound softer. Imagine giving feedback to someones presentation and would say "You spoke too fast". It sounds way softer when you say "You spoke a bit too fast."

Yes because a bit too much Is contradictory and for that reason funny. But in the end people can use both

A bit too much is more polite, it means its just too much not completelly, nearly means a lot. Too much is direct, means no dought is too much. I hope it was helpfull

Thenks Adam. I apreciate that.