....I am concerned about a lot of things. Will I be able, in the age of 17, to be a decent pianist?
....Secondly, buying a piano is financially challenging, so practicing on the keyboard(at least for 1 more year) while learning how to play the piano at the music school, can it even be possible?
Last but not least, what do you think about the books?
This is the first thing you need to address. It is not about becoming a decent pianist, it is about learning something that you are personally interested in and something you enjoy. If it is about becoming good or whatever, this is not a good place to draw inspiration from and I would advise not starting anything if this is where you draw your energy from. You strive to get better because you love what you are doing, you don't love to get better.
So long you can practice your fingering any cheap keyboard will have to do if you are strapped for cash. I have had students who practice on rubbish and come to me for lessons on concert grands, they obviously feel a huge difference, but you have to make-do with what you have. When you improve upon your instrument one day you will surely appreciate every bit of it.
If this teacher is planning to teach you from these books trust what they ask for, if they will no longer teach you I wouldn't buy the books. I personally find the Czerny can become boring, so hopefully you are not planning to do the entire opus, personally I like to use Czerny for sight reading work, but many teachers use it for technique and this is a traditional path to take to develop it with.
... Being a decent pianist comes from this urge to learn everything about the piano and understand music with my soul. Saying "I don't care if I am good enough" is hypocritical for me but it is not my top priority either.
.... Personally, I wouldn't mind completing the book. The more practice, the better- right?
It is good to hear that it is not your top priority, that is important. You would be suprised the amount of people who start learning something with the aim to get good above all else. Getting good (or better than others) is important but it is not our main motivation. But what do you want to be "good enough" for? To become a concerting musician, to teach, to just play all the pieces you adore, to become better than Joe Blogs, etc etc, I think that is a more critical question. Just to say you love piano music is great but is there anything else? Why do you love it?
Being "good" is a never ending changing target, I thought I was good when I was 9 and memorising Beethoven Sonatas, but now I look back and laugh at it. If we have a single vision of what it means to be good and we achieve it maybe we will no longer have the motivation to get even better. A pattern I see in some of my students, a few want to get better but the thought of getting better clouds their mind so much so that just to "get on with the job" first they must run through thoughts of how "good am I today?"
There is nothing wrong with setting yourself goals which once achieved would state to you that you have certainly got better, this is fine to motivate yourself this way but certainly it is the journey and the hard work that we need to enjoy more so, "the chase", if we don't then we will never really work hard enough.