hi, I did my GCSE maths last with the National extension college who I found very good, they assign you a tutor and you can contact them by phone, e.mail etc if you need help. You send an assignment to them and they mark it and give lots of feedback. On there website there is also a forum in which you can get advice from other students.
I have not used the ICS however I would recommend the NEC as the study packs are excellent and are even used by schools, colleges and children who are homed schooled.
I have to say the ICS did not appeal to me.
Also I would also recommend just starting with one AS to see how you find it and then if you enjoy it you can do more.
Also with the NEC you can spread the payments and pay by direct debit.
The most Important thing is that you need to be self motivated so if possible try to choice as subject that you enjoy or get a lot of rewards out of.
I don't like maths however I needed it get in to uni so that motivated me and I got a grade C after 6 months( at school I got an E after 2 years)
Good luck.