So just pay once for an entire year, if you use them often, or the flat monthly rate, whenever you need. This doesn't sounds too much of a hassle, especially considering the price.
I would say have as much fun as you can along side your studies. Really.
On the career side, experiment as much as you can in all the different areas (web programming, data science, ML/AI, game dev, etc.) and see what fits you the most.
I wouldn't worry too much about finding a job in this industry and I think focusing on your portfolio would make most sense only after you've found the niche that interests you most.
This comment resonates with me very closely. I majored in the humanities and honestly switched a few different careers in my 20s before settling on programming (long-time hobby).
You will probably find advice will be hugely varied and there is no single right answer. Ultimately your life is short and you should really plan around what you THINK will make you happy. If you get it wrong, no big deal -- you have the rest of your life to figure it out and you will probably find a way around to seeing what is the path of least resistance for you.
This is a good time to experiment and figure out what fits well for you.
I would add, have fun with other people. Make friends, make meaningful connections. These are harder to do outside of the university setting and this is one of the rare times where you are surrounded by a group of people with similar availability.
Additionally, work on your health. Get fit, learn to eat well.
Don’t overachieve, focus on the few things you are interested in and do them well.
