You should try doing a human next. I just got done working on a realistic human sculpt. It was really hard but I learned a lot and I was able to drastically improve my abilities in ZBrush and in sculpting.
Link to my ZBrush human model
https://steemit.com/art/@ace-bgi/zbrush-human-model
RE: Learning Zbrush 3D Modeling - First Creature Design!