As several have said touching the bumper in front is ok. Upsetting the kart in front of you is not. The earlier in your learning the more you will get it wrong. Own it and apologize when you do and work harder.
As far as being inside. In my first year, or maybe second I kept getting inside a guy and he kept coming down on me. I asked him if it was another racer named Chris on the inside would this driver come down on him.
He said. “He wont let me”.
I let him know some day soon we were going to wreck. Some day later we wrecked. After that he did not come down on me.
At some point with some drivers you have hold your ground so the other driver gives you the space on the track that you have every right to if you are up beside them heading in to a corner.
Learning to pass is a whole different thing than learning to go fast.