Milk- However many you fancy.......Most jobs list the standard 5 (including Maths and English ) on their requirements. A couple of exams per year for 3 years would get you 6. Talented children could easily end up with 12 or so if they wanted that quantity.
There is no way around it - if you want to do a particular course to get a particular career, then you have to do the exams. But you do have more choice of which exams and which levels you go for and when. For example, you can take GCSEs early and take a few each year. But it is best to take A levels all at once to prove you can handle the work load for degrees. But there are tons of other types of qualifications out there. It would be really dangerous to hide away from formal qualifications in the belief that home ed children have some automatic right to a job becuase they are motivated and clever.
What happens with qualifications/certificates when you homeschool? E.g. do kids have to do have exams or the equivalent? If not how can you show what you know on a job application for example when it says you need have English and maths to do a certain job? Also how does applying for universities work when you do not have ucas points?