Aqaaid

Q: If a Muslim mocks or jokes about a depiction of an angel like in a TV show saying for example it looks like something from a video game, is it kufr in any way?

Q: If you see a Muslim doing kufr by mocking Islam as an example or doing something else that is kufr, then he later does the 2nd kalima, perhaps for wudhu, but then gets informed that what they did in the past was kufr, is it fine if they just repent without doing the 2nd kalima again? If they don't, are they considered as disbelievers?

Q: If someone sins and they do not know that they need to change, and no one tells them, is the person still accountable and are their actions written as a sin?

Q: I am studying engineering at a University and have the following questions: 

As being physically present at classes is not mandatory, I did not attend these classes (due to laziness). Every lesson is recorded and available on the internet. During the classes the professor writes down some things which the students copy. These lessons are also available online, as you can basically go through the recorded lessons. However, am I allowed to ask a friend of mine who attended the classes to just give me his notes he copied in order to save time, as going through 30-35 recorded lessons (with each having 90 minutes)?

Q: I attend Madrassah for a full day and often find it difficult to sit in the jalsa position for long periods as I start to experience hip and knee pain. I was told sitting cross legged imitates the kufaar and not good etiquette so I avoid sitting that way. I also don't like to lift one leg up as I feel it's disrespectful to have the knee above the desk where the Kitaabs and Quraan are. 

What are some permissible ways to sit when acquiring deeni knowledge, this applies to even attending taleem and other programs besides Madrassah... and also, is it permissible for me to use a pillow under my hip (not for salaah) but in a program or in Madrassah?

Q: Are there recommended duas for the gregorian new year, i.e., 1st of January?