Dear dear Suze,
It is hard to think decide what to do with your life. Lots of people of our age are just drifting. I was lucky to find something I really love doing and am good at just before I had to make my decision. And even then, I still sometimes think that I am drifting, waiting, searching. So it is great that you have figured out what you want to do, what you love and what you are willing to work for.
I also believe that having a gap year is a great way to get to know yourself better, to find things out about the world etc. But I do understand why dad is not too keen on it. Also, I think that, yes, a gap year could contribute to your personal development, but only if you really want it to do so.
So, what I advise you to do, is to make a list of the things you could do, and then make a businessplan for the year. It's just a proposal, so it could be very sketchy, but try to set goals. Also, you might consider getting a job, if only for the first half year. You could maybe want to get money for your travel, or for your future study, or it could just be to keep some structure in your life. Believe me, freedom is great, but sometimes it can also be great to have something to hold on to. Be sure to pick a job that won't take time after work, like school does. Then it won't interfere with your music. (By the way, it is also good to set targets for your music too.)
Making a plan will show dad that you are serious about it, and it will force you to think things through. You have to fill that gap year, cause otherwise it will account to nothing and you don't gain anything from it.
By the way, there is something I found that is just for you (I like it too, it has Lord of the Rings and pretty pictures of books and nice quotes from John Green). It is the tumblr that is actually connected to 'The autobiography of Jane Eyre', a 'Lizzie Bennet Diaries' inspired webseries. I haven't read the novel yet, so I am not quite sure if I'm allowed to watch the series (I have only watched the first 4 episodes), but I'm sure I'm allowed to look at things that make me happy. http://eyrequotes.tumblr.com/
Did I mention the Smiths are there too? They are! It is great. Just check it out! And it goes on forever and ever... I still haven't found the end.
ps. If I have time I will post another, official blog on Sunday. But I am very busy writing an essay (actually two! Ah!) at the moment, so maybe not...