2:51 AM, Tuesday October 13th 2020
I appreciate you limiting your questions to the important ones, at least right now - I still have a couple homework submissions to critique before I can get to bed tonight, and unfortunately to ensure that I don't miss any responses, the system actually forces me to respond to them before I can grab the next submission.
Here's how I would approach constructing that horn. Keep in mind this is not a specific approach (especially in terms of the additional forms I add in the third and fourth steps), and it is not the only approach, but the gist of it is there. Construction is something like a puzzle - you have pieces you can use to move towards your goal, and so you keep using them until you get to an approximation of you're aiming for.
Edit: Sorry I missed your other question. If you can see part of a form, you should draw the whole thing. That doesn't necessarily mean the whole leg, but don't draw part of a form so it gets cut off where it is not visible. If you can't see any of the leg, you don't need to draw it.