That's not necessarily the case. If you have a strong Punjabi base, you read Punjabi literature in addition to Gurbani, you read Punjabi non-fiction like books and newspapers, watch Punjabi-language news and you listen to katha, I don't think you need to watch Punjabi movies.
However, if you do none of those things, then Punjabi movies are a good starting-off point.
Agreed. It's pointless to say, "well 10 were needed because they were doing different stuff."
I mean, it's OK for us, since we can see that our Gurus did do varying things. But that's not the question the atheist is asking him. The atheist is wondering why in the world there needed to be 10 in the first place.
The better answer is: Why not? I'm mean, if you don't believe in God, fine. But if God does exist, why does it matter if he deputed 1 Guru or 3 or 10?