will ofsted want to do an inspection for me, even though I hven't been looking after under 8s? I have had two over 8s four days a week but not in holidays...?

if your are on all registers then yes you will need a inspection.

how details obs do they want then for over 8s? I'm at a bit of a loss as how to compile such info....i kept details of what they did, how they acted, what they ate etc - is this enough?

You might be able to put them off for a little while if you are expecting some Eyfs children to sign up soon. :D