Nope Joseph is wrong
“”what siddur/nusach does bobov use”
Nusach Sfard.
Incorrect. They have a tzans nusach the siddur used in shul is Tzilusa d’Shlomeh. While being quite similar to nusach sefard there are differences. For example they end Atah Chonen with “deah binah vehaskel” unlike nusach sefard.
“where are the biggest communities”
Boro Park, Brooklyn, NY.
Correct
“what differentiates it from other chassidish sects?”
Who said they’re different?
All Chasidish sects are different. See above regarding nusach. bobov wear tefilin on chol hamoed prior to wedding (granted this isn’t limited to bobov but most chasidim don’t wear tefilin on chol hamoed). There are of course differences in dress compared to say Satmar. (I don’t think they wear bow on hat on Left like viznitz does (also tsanz) but im not sure)