All I can speak of is my truth as I remember it... I knew that baptism was the way forward upon accepting Christ as my saviour, but at that time I was not able to articulate the depth of the decision which is why I did not write about it for that point.
I was 12 when I was baptised, so at the time my understanding was very simple, I had knowledge of what I believed, and I prayed for a sign, specifically for a sign that I would recognise as "the" sign. And then on hearing that a friend was being baptised I felt absolutely sure that that was my next course of action, not because my friend was doing it but because it is what is asked of us and I believed it to be my answer to prayer.
I already stated what Jesus did for me, he died for MY sins, to accept MY punishment on himself in MY place, so no. Nobody could do that now. Jesus lived a perfect life, fully man and fully God so that I may be reconciled with a perfect God despite my failings.