Hi Amin!
It's good to arrive at least one week before the introduction, so you have time to get familiar with the city. When I started, I arrived around mid-August.
You can get an impression of how the academic year looks like here: https://www.youtube.com/watch?v=EV5uS067ECg&list=PLVxbxX3iRJ2TQv9VYlk8-GtFb8qxS6DpJ
And regarding internships: It depends on the company.
Most internships pay a (small) fee, but it depends on the agreement you make with the company.