If Local Transforms is on (found on the right shelf, or in the Transform menu), then zbrush will focus on the point where you last clicked on the model. So if you want to zoom in on a character’s finger you would just need to quickly tap on that finger, and then you can rotate around it or zoom in on it regardless of where your cursor is.
If you wanted more mouse navigation options, you could try https://draster.com/ZSwitcher/ (although there is a cost involved). Personally I’m a fan of zbrush’s default right-click navigation. It’s basically designed for tablets/styluses in mind so you can do all your camera movements with one keyboard modifier and one stylus button, and it winds up being pretty fast as a result.
Lastly, I think part of the trick to understanding Zbrush’s navigation is to realize that you’re not moving a camera through a virtual environment to orbit around the model. Instead, you have a 3d model essentially floating in a tiny bubble above a 2d painting canvas. You are moving, rotating, and scaling that bubble in order to get the view you want while your eyes/‘camera’ stays locked in place.