WE DON’T HAVE TO OBSERVE (say Selichos etc) ON BEHA”B
Regarding fasting: the Aruch HaShulchan already said that few fast Behab, and Chassidim in general weren’t into fasting (outside the fasts which are Mechuyav Al Pi Din, see Kesser Shem Tov, where he writes that it’s much better to invest your energy into Torah and Davening over fasting Chassidim were also into serving Hashem with joy), and it seems that nowadays non Chassidim also advocate that Teshiva through Torah study and Chessed is better than fasting (I’ve seen it referenced to קריינא דאגרתא ח”א עמוד קפב אות קסז, but I don’t own a copy to look it up inside).