depends what time he's leaving. if he can aim to be on the road from any of those villages by 730am then he;ll hit the m40 j11 in 10-20mins max.
if you need to be going through the town from 8 onwards then he'll be queuing.
for deddington/adderbury - never go through the town, go around either towards train station.
the deddington/adderbury road gets very busy when the M40 has an accident between j11 and j8 as its the rat run for oxford and bicester.
accidents don't happen so often at the moment but before christmas we were on average sitting in two accidents a week during our commute (J11 to J8a) - usually one in each direction.
where is DH heading from the m40? we do oxford in 50mins on a week day leaving central banbury at 7.55. friends do south birmingham (bourneville) in around 60mins, leaving at 745
not sure on schools - have had friends who moved to Adderbury and didn't get places in the local primary school, all be it a stones throw from their house - they were taxi'd back to banbury schools.
bloxham - the secondary - warriner is very popular, you do need to be in the village to get in.
deddington and bloxham have more shops, pubs etc to adderbury. deddington also has a very good farmers market.
oh in the bad weather (snow) you'll always be able to travel the adderbury/deddington road as the main gritting plant is on it. bloxham - you'll be snowed in.
if you want a slightly bigger villages/town but with more choice but easy access to the M40 have a look at Middleton Cheney or Brackley.