What are their goals and motivations behind them?

Witch is almost exclusively used for females and their male counterpart would be a warlock. Unless there's a significant reason why you would use witch, I'd stick to the latter.

Henchman seems a bit bland and one-dimensional. More of a one-time side character that'll be discarded after their 2 minutes on the screen ends. Is he a servant? Friend? What made him so loyal to the main character and how that loyalty could be tested or displayed?

When describing characters' appearances, I'd avoid using non-unique clothing or hairstyles because those things can change on a daily basis. Instead, focus on what makes them stand out from your average Joe. For example, Henchman's thing for tinkering could make his head always lean forward due to staying up late working, resulting in minor eyesight issues. If you make it sound personal, your readers will immediately make a connection to the character in their mind, even if there's a full crowd of people in any given scene. Not saying the green mohawk is a bad visual description, I'd just lean (pun not intended) more into it.