Really exciting that you are thinking of studying illustration!
Having strong fundamentals such as anatomy and environments is great.
Being able to also demonstrate strong narrative and storytelling with your work would be good, as often with illustration (say if you were to professionally do commercial work for a publisher/creative agency) you will be given a brief (aka a description of what they are looking for, with ideas about brand identity/guidelines, their target audience etc), and then it will be up to you to create a few different pieces and take on their feedback and incorporate that into your overall piece/s. So being able to show in your portfolio your process of working - how you get from A to B and how you adapt.
Being able to show different angles/perspectives is also really useful as well (e.g. if doing landscapes). If doing character related work very useful to have a mixture of appearances, ethnicities, ages, as well as different angles for that person. Although developing a strong personal style is key for illustration, also being flexible with the kinds of content/subject you are creating is essential for people to know you can take on different tasks easily.
With illustration/art in general it is also really useful to early on be thinking commercially. So with illustration you are going to likely want to think about developing web skills (to have your own website with a portfolio), to be up-to-date on basic law around copyright, to understand how AI systems may use artwork and to protect yourself from that, understanding how contracts work (especially if you delve into freelance work which a huge % of illustrators do), how to boost your profile on social media (not essential per se depending on the nature of the work you do), and how to manage your time between admin + creating.
Good luck with everything! Hope it goes well, let me know if you have any other q's if this has been helpful