Re: Tarawih - Wajib or not
AKB has posted Ahadith that show Prophet pbuh did pray tarawih for 3 nights in Ramadan and people prayed behind him (in congregations). People WERE praying Tarawih in small groups as written in Hadith you posted, all Omer ra did was to ask them to pray under one Imam instead of small groups, how does this become a Bida'ah?
Rasoolullaah pubh cried once on Shahadah of Imam Hussain (according to some narrations) , now if some people cry every year on the same day in large congregations, is this a Bida'ah?