Yes, my dd is doing the Bucks test. So far I have been looking at individual question types and we are working through them gradually, practising each type from the IPS papers. Once she has learned the technique I'll let her start working through whole practice papers so that we can work out where we need to focus our attention. I've also got the Tutors software for her to practise on later as I understand that this helps with improving speed. We also need to do some more work on vocab - her general level seems to be quite reasonable but she too occasionally comes across an unknown word.
I think you are right to say that there are only six questions of each type in the test, apart from Zs of which I think there are two in each paper.
My dd is lucky in that several members of the family are able to help her with her preparation - she gets me most of the time
but her dad is good at showing her how to do the maths-type questions (eg type K) and her big sis did the test a few years ago and can help with anything, but is particularly good at codes. She really wants her sister to join her at her school so will happily sit down and share her own expertise which is based on first-hand experience
An added benefit, I find, is that a change of face/voice helps to keep dd2 interested!
Good luck, anyway.