For chat system you don't. However you must have answered correctly the randomly generated question the ninja asks you once first.

I have not tested the sweep function but i doubt you would loose anything at all. You need to clear it once before sweeping so you have proven you can beat it.

That's odd. The cat has a fixed amount of coins attached to the health it has. You shouldn't be able to get more or less on that one. Also i'm surprised you dont get materials when you sweep exp. Will try that tomorrow