He was enlightened on the 20th October.=)
Guru Nanak Ji became a guru in April 1469.
Guru Nanak became guru because, he believed in one god and that Muslims and Hindus should not be separated and should be united instead. He went missing for 3 days at the age of 30 and was found that...
Yes, Shri Guru Nanak Dev Ji was the first Sikh guru.
Guru Ram Das ji became Guru on 30 August 1574.