CH have set up an extra open day tomorrow afternoon (you had to register by this morning), did they forget to contact you about that or does it still clash? If they've not contacted you and you could fit it in, I'd ring them immediately and try to get them register you (you can square things with your son's school in the morning!).
Regardless: Birmingham Admissions might like forms in by 1st Oct and might do their best to imply that you have to do it by then, but the Schools Adjudicator made a decision against them on that a couple of years ago and on top of that there is now a national closing date for forms - you have until 31st October (as you can just about
tell if you read the transfer book carefully!).
I have an open mind about whether FW is more relaxed - I'll never have first hand experience, but from talking to parents I would say FW seems more driven than CH - even before day 1 (i.e. three hefty projects in the summer holidays before starting in Y7!
- ours didn't have anything at all). "The bare minimum" would be an unimaginably intensive level of effort for our son but as far as I can tell he seems to be getting the hang of CH (at least, we haven't had any letters or phone calls...yet