1. Pressure control, remember that these are exercises so the idea is to try, and over time you'll get better at it. There's a lot of ranges of thickness one can get from a 0.5mm fineliner (which is why we use them) but it's something you unlock over a lot of mileage and experience.

2. Mandatory for the organic forms with contour line exercise, because it helps with what that specific exercise focuses on. Again - each exercise serves a purpose, challenges you in different ways. So each exercise has specific rules depending on what it's designed to focus upon.

3. It all depends on the nature of the form - a contour line wraps along that surface. Our sausage-like organic forms are made up of circular cross-sections in one direction, which allows us to explore contour lines in a simpler, more narrow scope - as ellipses. But not all contour lines are ellipses, they're all gonna be determined by how that surface exists in 3d space.

The thing to remember in general is that the exercises we do help develop specific areas of your spatial reasoning skills. Bit by bit and from different angles, this advances your more general, instinctual understanding of how the things you draw on a flat page exist in 3d space.

These are things the exercise develops in your subconscious, so focus on doing the exercises as they're instructed, and don't worry too much about trying to consciously understand how it all works in practice. The goal is that when you're drawing your own stuff, gradually what you learn here will influence how you think about it and how you naturally approach it, so your conscious mind can remain focused on what it is you wish to draw rather than how.