I'm doing line art for a sketch that I already created in Photoshop. When I imported the drawing into Illustrator and zoomed it to 100%, I noticed that it was a lot smaller than how it appeared in Photoshop. I did the lines for one of the characters so far while zoomed in to about 200% since 100% made it difficult to see all the little details. However, when I zoomed back out, the lines appeared thick and jumbled together. You can see what I mean below. Am I supposed to do the line art while the document is zoomed at 100%? How am I supposed to see all the smaller details? Basically, I want the Illustrator lines to look almost identical to the Photoshop lines.
Draw at whatever scale you like and you feel conformable with.
Since art created in Illustrator is vector in nature, it can be rescaled when you are done to whatever size you need without any quality loss.
Typically, when I place something in AI for tracing, I enlarge it to 200% or more in Illustrator, then manually trace it. I do not zoom in. I enlarge the placed image.
You may feel your paths are "thick and jumbled together" depending upon the stroke weights and the pixel density of your monitor. If all the strokes are less than 1pt in size, when zoomed out, the monitor has no choice but to use the smallest unit it can to display them - 1 pixel. That may make paths look thicker primarily due to anti-aliasing for display. Also a good reason to work larger if you can.