Before you go any further think about entry fee costs. You really do need to budget for these well in advance.  There is a general misconception that public exam entries are free of charge but this is not correct; they do have to be paid for and you need to give this plenty of thought; schools cover exam entry fees.  Entry fees are per subject and not per paper. Some, but very few LEAs, will offer support for English and Maths but this is uncommon.  You may well need to plan to include overnight stays near the exam centre.  It is not unheard of for parents to have 20 visits plus to an exam centre in one exam season.  The temptation for many home-educators is to trim back the number of GCSEs/IGCSEs to fit their budget but this will disadvantage a child who is aiming for a place at a good university.  The minimum requirement is five GCSEs but most applicants will have at least nine.

Note that most qualifications have multiple papers that students will be required to sit.