I'm not a scholar but I suspect that Jesus responded as a rabbi might. The custom was for potential disciples to approach a rabbi whom they wanted to follow. If the rabbi was interested he'd ask them questions to determine if they were suitable cantidates. If not be would send them away and they would go home and take the trade of their father. If he accepted them, he would say, 'come, follow me' and they became the rabbi's disciple.
One teaching technique that rabbis used was posing questions. He would ask a questions his disciples, and the disciples would debate amongst themselves and the rabbi would listen. When he had decided the correct answer, the discussion was over and the disciples accepted the rabbis judgement.
To us it seems a counter intuitive that asking a question is how others (not the asker) learns. But this idea was understood by those living at Jesus time. That's why when jesus was 12 he was found at the temple asking questions of the teachers and they were amazed at his knowledge. He wasn't learning from them, he was teaching them. Likewise, when his disciples finally realise he came from God, they said, 'now we know that you know everything and don't even need anyone to ask you questions.'
So I really don't think that the question was a rhetorical question for emphasis, meaning, 'Of course I'm not God! I'm not that good!'
Instead it was probably a combination of a job interview and a teachable moment. I'm not sure if the rich young man intended to offer himself as a disciple of Jesus (it seems pretty clear that he was genuine in wanting to know how to secure eternal life.)
Either way Jesus answers by inviting him to be his disciple, beginning by testing his theological knowledge and teaching about himself, 'If you want to be my disciple, the most important requirement is that you know who I am. Here is a riddle to get you thinking: if I am good, and you said I am, and God is one, and only God is good, then who am I?'
He then concludes by testing the young man's ability to forsake everything for him, and invites him to be a disciple, 'Come, follow me.' Thus he answers the question in two ways, firstly, 'Believe that I am God,' and secondly, 'Be my disciple.' (Both of these are the same thing-- following the commandments wasn't enough, following Jesus is the greater thing, therefore Jesus is greater than the commands of God, therefore he is God.)
I disagree that this is an example of Jesus perceiving a difference between himself and God the Father. Whenever Jesus is talking about what is required of people to inherit eternal life, he always refers to believing in him. For Jesus to say anything different on this occasion is contradictory.