1. I will assume my room as pure as it was najis because he came from kafir washrom with wetness and later he walked over my room with same wetness. So what mutanajjs is my room, second or third?

2. Leather from Brazil, Portugal and Italy, is there good probability that the leather is from halal source or not? I purchased it from UAE. i cannot assure what's the probability.

I am confused with the law of medium of transfer najasat.

3. I think I touched a kafir with wetness and with the same wetness I touched my car steering. Now later on again I touch my steering with pak hand. Did my hand become najis or not?

Follow the general rule that everything is pure unless proven najis.

As for the last question yes your hand is najis but that would not transfer again