We call it a crayon in the UK :)

If you must do something it is more important than when you have to do something. If you must go to the doctors, it is more important to go then when you have to go, there is more emphasis to 'must'.

The first one is the best suited as there is emphasis on the fact that you were talking exactly about the subject

'There is more to it than meets the eye' is when a situation is more complex than you think it is, your sentence says the opposite, therefore what you see is what you get, the person or situation is not complex, it is the opposite, it is simple

From the context, it would seem that here, 'funny' means, strange/ weird, something between them is off and not quite right.

Troubling means: causes distress or anxiety. For example: "The question was troubling" means that the question caused the person who heard it to be distressed or anxious. So, in this context "This question was never more troubling", it means that the same question has been asked and heard before, but this time, the same question causes anxiety. For example: the president may be asked a lot "what should we do about this problem?". However, if the president is asked that when the solution to the problem could have serious effects, such as war, for the president, that question had never been so troubling - before if you asked, what should we do about the problem and the problem was what to cook for dinner, there would be nothing troubling about the question, however, this time, it causes anxiety.

Not at all. To make it absolutely clear I would say: 'The amount of paper produced each year is three times the weight of the vehicles manufactured worldwide'. I've used a synonym here for produced to vary the vocabulary and the passive language to make it more direct.

Also, close: 'to close a door' uses a Z sound. The 'S' is not always hissed :)