Hi there, I don't know if it's any help but my daughter (age 14) has just taken IGCSEs in Biology and Geography, and GCSE Maths.
We used Cambridge (CIE) for the IGCSEs. I'm not sure why really, I think because there was a general feeling that they are better thought of than edexcel, but I don't think it really matters. Also the schools we found near us who would admit her as a private candidate do CIE.
We did AQA GCSE for maths becuase there's no coursework so it's easy to sit as a GCSE.
We had no tuition at all. We bought a book for each subject and worked through it. I'm not in a position to afford tutors for anything so it put us the position where we had to give it a go!
As it's exam only, we have no idea yet how she did! But she thinks the Geography went really well and the Biology not so well, so we'll see. Maths is modular and she got 100% in the first module and 98% for the second so she can do pretty badly in the one coming up next week and still do well - we basically know she's passed that already.
Generally, I'd say it was much easier than we anticipated. We did it in a year from start to finish with really not much work at all. This last month has been hard going revising for them, but up until then she probably only did about half an hour a day on each subject, if that, and not every day of the week. So you'd easily cover subjects in a year.
Just ask if you want to know anything else!