From the sounds of it, his service will probably be a sound cloud for new/aspiring artists. This would certainly negate the need for any music rights, as the artist will be doing anything to get noticed and will probably make an agreement with the music service to allow the sound cloud to use their music as and how it wishes.
OP, if this is the case (I may be jumping the gun a little), but the easiest way for any aspiring artists to get noticed is by recording something and putting it on youtube. IF yours is a sound cloud, how is your service going to compete against youtube?
Like many ideas, your idea will probably not see the light of day (don't take this negatively...but this is a fact). The reason for this is that there is much hard work involved in getting an idea off the ground, ie. the implementation. It takes a very special character to take risks and launch an idea/business. In many cases, the idea is important but the implementation is just as important, if not more important. If this idea is going to really happen, then you will be getting very little sleep, you will not be going out and you will be working like a dog. Initially, until you idea becomes big, you will be poor. You will earn far more working at McD's than working on your project. However, the hope is that your idea explodes and you become a millionaire
Another question: if your idea really is that good and you have confidence in it, why the devil are you bothering with A-Levels?
What you should do is take a couple of years out of study and see if this idea picks up. If it does...you will never have to do your A-Levels. If it goes nowhere, then you can goto college, start your A-Levels then goto Uni, etc.
Somebody earlier mentioned that there are trusts set up to advise on startups. I would definitely look into that as these advisers can help prepare your business plan and get you thinking about your idea from a business angle.
Good luck man...and all the best.