to even be considering this (private school related)?

[pickledsiblings]

40 minute drive to a Park & Ride

20 minute bus journey

10 minute walk

Would I be insane to consider doing this with my 7 year old as a daily commute/school run (and the reverse journey home again)?

School is a-maz-ing and just 'round the corner from potential new job.

It doesn't sound like any of this is logistically possible pickled unless you move to Cambridge nearer your prospective job so that you are not commuting so far.