In answer to your two questions: Yes, it's only used for something negative. No, you can't be notorious for being altruistic. Famed, famous, well-known, renowned, well respected etc, but not notorious. 'Notorious' means well-known, but always something for something bad. A notorious liar, a notorious womaniser...

That sounds good.

Yes

I have only heard it used here in America in a bad context. MW's definition also says, "generally known and talked of; especially : widely and unfavorably known".