Hi Pesto,
(A disclaimer: English is not my native language, I hope it’s still legible)
TL;DR: Learn in Blender (sculpting and retopology), then think about ZBrush if you feel you have outgrown it.
I’m a newcomer to Blender (about 2-3 months), a beginner in sculpting (about 2 weeks, after watching YanScult videos), and a fledgling with ZBrush (bought it over a decade ago in a sale, but only actually used it for the past few days).
Thus, me giving uninformed advice is dangerous and probably unwise. So here it is.
Sculpting in Blender relaxes me. I gotten used to Blender’s UI and UX, and feel comfortable with it. YanSculpt’s results are without a doubt the proof that you can achieve awesome sculpts with Blender.
Very recently, I decided to give ZBrush a try… after all, I own it (thanks to their free upgrades, even from the time it didn’t actually cost much).
The variety of matcaps is refreshing. This might sound stupid, but Blender is really limited in that area, and matcaps can help a lot when sculpting. Eevee might change that.
You also have tons of brushes. For example, sculpting a rock feels easier because of the different “trim” brushes, making it much easier to get nice crevices (most of these brushes are hidden, not in the main palette).
In short, I feel ZBrush to be different, and offer more possibilities in some areas, which might help (or confuse). It can also handle millions of polygons, unlike Blender. But you speak of games, thus I doubt you’ll get to that point.
However, ZBrush’s UX is abysmal, and its UI is the most confusing I can remember (I’ve been in computers for over 30 years, on many different OS… I have seen weird stuff). As much as I enjoy swiping a pen on the tablet in ZBrush, everything else amply compensates in terms of stress.
You claim to enjoy using Blender, which means you are probably quite used to it’s interface, rotating the viewport and so on. Getting as comfortable with ZBrush might required a solid investment in time.
As for retopology… I don’t have much experience with that, but it is my understanding that you cannot get proper, game-ready, topology using (semi)automatic tools without first having a solid base of topology.
So my advice would be to first learn how to do topology manually, then integrate tools like Bsurfaces or RetopoFlow (free on github, and once you get awed by its awesomeness, you can buy it to help further development). There are many others, but RetopoFlow (2.0) seems amongst the best.
Then, you might have a proper look at what ZBrush offers, and you might ultimately decide that the tools in Blender are more interesting.
Or you might go for tools like Topogun or 3D-Coat, which seem quite popular amongst ZBrush users.
If most of your instructors are using ZBrush, obviously that might be enough to buy and use ZBrush. Using the same tools your teachers use can certainly make things a lot easier.
Personally, though, every course/tutorial I followed was easy to translate to Blender, once you get the hang of sculpting in Blender (YanSculpt’s daily tips helps a lot for this, although you quickly get to a point where you find the music annoying and repetitive!).