If you go to the Redbridge website (www.redbridge.gov.uk), you can check out the catchment area for Ilford County High - if you are outside the catchment area, then as it is hugely oversubscribed, you wouldn't in my opinion have a chance. The Redbridge 11 plus by the way, is also the most difficult in the country
My friend's son is sitting the initial 11 plus entrance exam for the Latymer in Edmonton: (www.latymer.co.uk/) Their 11 plus exam is different to that in Redbridge but there is loads on their website. From chingford, the journey there by public transport dosen't appear to be too bad.
Most people either do practice papers with their children or have them tutored, usually from Year 5 onwards. You could have your ds assessed to see if he is up the mark though. Redbridge 11 plus consists of two papers in Verbal reasoning and non-verbal reasoning. To be fair, you do need to have practised these before sitting the exam as they are nothing like the general curriculum work covered in school. Independnet schools do prepare the children for these exams but state schools don't. Check out this website for their 11 plus forum - it is full of interesting info from very involved parents but you might be enlightened!
www.elevenplusexams.co.uk/
Schools have series of open evenings in September/October every year prior to the deadline for secondary school applications, so you could go along to these yourself next year. While they can be a bit staged, you do get a sense of what the schools are like, how organised they are and what the pupils are like. There's nothing like quizzing the pupils who show you around!
Regarding choice, it is a bit of a myth that you have loads of choice as to be perfectly honest, the successful schools are always oversubscribed and will only then take children from an ever decreasing catchement area. You might be lucky though and find you live in the catchment area of one of the schools near the top of the list I gave you. If ds is a bright boy with what is obviously an interested parent, then he'll do well.
If I were you, I'd check out the local schools and find out which would be your catchment area school. Phone the WF education authority or check their website for these details. Chatting to parents at the school gate is another good way of getting feedback based on personal experience. You could also ask at your ds's primary school, regarding the common secondary schools that they feed into.