You do two years of Sixth Form, Year 12 and 13. First year AS, second year A2 which makes up your two parts of three full A Levels. That's the standard anyway. I did three years though and some people do extra for a variety and/or combination of reasons; poor grades/not ready for uni/not sure what they want to do/want to get another qualification, but you'll mainly do two years and then progress to uni.
As for the rest, I honestly really wouldn't bother thinking about it until you get to Sixth Form which is when they'll start helping you with all of this anyway, from fees to student finance to UCAS, everything. Concentrate on what you want to do at GCSE leading into your A Levels and then when you reach that stage start looking at the next level of your education which is university. One step at a time, too much changes year by year to plan so far in advance in my honest opinion. And if you're in Y9? I think then you've got four years to wait until uni by which point after four budgets who knows what this government will have done to the education system
