We're looking into home tutoring too.
There are many parents who contribute in this site are parent tutors including myself. I have tutored my children to Tiffin boys school without the help of any external tutors.
Note that both Tiffin schools conduct the exams on the same question format - NVR and VR. NVR 80 questions in 50 minutes; VR 85 questions in 50 minutes.
It is very much doable if you have the time, resources and the knowhow.
When did you start / books
Among other factors, it mainly mainly on the child's ability. If you are planning to start from year 5 then you have plenty of time to start from the basic and gradually grow with it.
books did you find most helpful
All the free downloads available from this site and others.
How to do VR from The Tutors (available for free download from this site), Athey and Learning Together.
How to do NVR from AE Tuitions 1&2, Bond
NFER practice papers on VR, NVR
Susan Daugherty/Bright Sparks
..and many others