Hi OP. I hope the following helps:
First go to the website of the school and check out which papers (e.g. VR, Eng, Maths only or NVR too or writing paper too) and the format of the 11 plus e.g. multiple choice or standard, plus the duration of each paper and the relative weight given to each paper.
Second. Starting in Year 5 is fine. If your child sits the exam in the Autumn term, there is ample time to prepare and familiarise with the process.
Third. Preparing at home without a tutor is fine too as long as your child genuinely is motivated to sit the exam and is prepared to go for it. Some kids love VR for example and it can be made into a game.
Fourth. In addition to preparing for the test, keep injecting lots of fun into it e.g. go onto fun websites www.thelogiczone is a good one and do logic puzzles from the newspaper. Write fun messages in code to each other - and change the code logic often...do treasure hunts with coded clues.
Fifth. For Maths, Eleven Plus Exam Group (search online) does good practice papers. For Verbal Reasoning, the best we found were those published by Walsh (again, search online). Bond is good for English papers.
Sixth. Read to your child the books that may just be a stretch so that you can enjoy literature together, talk about it and extend vocabulary. Go to the library and feed the reading habit. Put a dictionary by the bed.
Seventh. Start off with a few untimed (leisurely pace and spaced out over days) practice papers PURELY to assess gaps and so you know which areas need work. Thereafter, don't spend hours doing exam papers. A few weeks before the exam, do a dummy run under exam type conditions. That way, little details can be ironed out.
Finally and most importantly. Keep the process pleasant and unstressful. Don't practice when your child is tired or desperately unmotivated. Keep the sessions short and pick your moments! Make it clear that this is a journey that can be fun and that the journey is far more important than the exam. Stress and disappointment are crushing. Your child will learn so much from preparing for the exam, that whatever the outcome, you will have provided a wonderful foundation.
Bonne chance!