Aqaaid

Q: I read this somewhere:

Also, As-Suddi said, "When a man would come to the two angels they would advise him, `Do not fall into disbelief. We are a test.' When the man would ignore their advice, they would say, `Go to that pile of ashes and urinate on it.' When he would urinate on the ashes, a light, meaning the light of faith, would depart from him and would shine until it entered heaven. Then something black that appeared to be smoke would descend and enter his ears and the rest of his body, and this is Allah's anger. Isn’t Allah’s Anger His Attribute alone so how would it enter a human being?

Q: Is it true that when you are not certain about some fact in Islam then you don’t believe in that? For example, if I don’t know about a ruling in Islam, I don’t believe in that?

Q: Which one is the shahada? Is it “lā ʾilāha ʾillā llāh muḥammadun rasūlu llāh” or the sentence in tashahhud “Ash-hadu an laa ilaaha ill-Allaah wa ash-hadu anna Muhammadan ‘abduhu wa rasooluh”? I thought they are the same but not sure. Which one should a new Muslim or a one out of Islam to say to become Muslim? 

Q: I recently was asked by a non Muslim if I can tell him the shahada to make him become Muslim because he wanted to become Muslim. So I told him the shahada in Arabic and also in English and explained what is Islam and what you should believe in to be a Muslim. He did it and he believed on what we all Muslims believe so he became Muslim.

After some time this guy asked me that someone told him that the shahada you believe and the things you believe in that the other guy told you. With that you can’t become Muslim because everything he told you is true but you must go to a masjid and repeat it with the masjid Imam so he can repeat with you then you will become Muslim. The other guy took him to a masjid and the imam repeated the same things.

My question is that is this guy became Muslim the first time I repeat the shahada with him or no he became Muslim when he met the masjid imam which one is truth  Can someone regular not an imam make someone become Muslim ? Or no only imam can make someone Muslim ? Am I sinful because I told him shahada first time and he believed it?