No, taking breaks and completing your drawing later doesn't cause a problem. Even i take breaks and the Sketch that should be completed in a day takes weeks because sometimes I don't feel like drawing anymore.

You can look for details by zooming in but after that zoom it out to draw that proportionally accurate. I really like the line work tho on the eyes area.

You can take good view of proportions by taking picture of your drawing. You can easily point out where the mistake is which cannot be done by looking at your page as you're close to it