OP, everyone's experience is unique. You could "categorise" them in certain ways. But ultimately, it's a combination of many factors. You can't rely on one or a few pieces of advices. Do need to have a proper think about your child, your goal and the "what if" scenario.
In certain regions, grammar schools take on 30% of the students of the area, whilst some regions like north London could only take the top 5% - 10%. So someone suggested earlier on that Bond books are the best, which might be true for their experience, but it can be very misleading for those schools who take on the top 5-10%. Bond books are too easy and definitely not sufficient to support the superslectives.
While some parents were successful self tutoring, it may not suit all. Depending on the time, your own capability to tackle the exam contents and especially your child's learning style, there's a massive difference of feasibility in one way or the other.
My child would not have worked with me alone, if they didn't get tuition. The dynamic was just there to aid the process. The poster managed to do everything themselves without outside help has a lot to do with the children themselves.
A lot people said no matter what you shall never be entirely disconnected. You know your child the best and to find what works for them, it takes more than a few hours a week by a tutor. But of course, again, it depends on the child (I'm probably not talking about the genius type who don't need to work but can get in wherever they want. Most kids aren't genius...)
Don't do paper too early. Try to focus on building up the solid elementary blocks and read LOTS. Vocabulary is really one of the key things and reading help builds that (and helps with creative writings too).
Good luck.