Sorry you've found yourself here, but hopefully you'll find it useful.
"my child wasn't tutored" is quite a problematic statement at an appeal.
For a start, how will the panel know you're telling the truth? One of my colleagues used to ask "was your child tutored" at appeals, and quite often parents answered "No". Now I remember a friend chatting to me one year after that batch of appeals, and she said 'I hear you allowed the appeal for little X' (a child at the same school as her daughter). "Yes, we felt sorry for him as he'd had no tutoring". "Like **** - he was down at the tutors at least once a week, and in school holidays". What could I say - we'd been duped - parents will often do anything to get a place, including lying to a panel.
It's probably worth mentioning in passing, but you won't be able to base your appeal round it. Panels are not there to judge the parents.
If the school has a specialism and your child is talented / interested in that, then certainly that's good to mention. So with G5 music, a 'photocopy of the latest exam certificate would be nice, but not copies of every grade certificate he's had or programmes from concerts (too much information). Likewise if a child is G&T at say rugby (and the school specialises in sports), then a mention that they're playing in the county squad is good. Having achieved a high score on Wii Fit might not be so useful
Make sure you get together the academic reports - such as the L5 in Y5 SATS that you mention - you need to show that the exam result was not typical of your sons capabilities.
There's a child in my daughters class who has exactly the same problem as your son - bright enough, but not tutored, and just missed a place. Make sure your son is also on the waiting list if he passed the exam but the school was oversubscribed.