Re: serving alcohol
A scholar told me that there is a hadith which specifically addresses the people who only try to rely on Quran without consultation of Hadiths. For such people he said the Prophet (saw) told the believers to ask those people, " Is donkey halal or Haraam ?" (Prove it from the Quran)
Besides that, minor details of namaz, wudhu....etc. are not mentioned in the Quran, hence should be understood from the hadiths.
And Allah (s.w.t) knows BEST!