sense understands the number of new houses proposed is circa 218.
We estimate an average of 1.85 adults and 1.5 children per household. (Yes, Bucks. Grammar schools are a good draw, aren't they?)
So that would be 403 adults and 327 children.  Total 730.   Roughly.
Then there's the residential home and sheltered housing. Another 155 adults. Total 885.

Schools
So, approx. 80 pre-school children and 125 in each of primary and secondary education.
The 125 requiring primary education equates to 20 in each of the school years. This is roughly two-thirds of a class in every year. Both Robertswood and Middle School are full and we understand they see no short-term diminution in demand. Neither can readily build another 6 classrooms (i.e. one per year) so if the NSE's scheme goes ahead, there's going to be massive competition for places. Any CSP residents with very young children and/or planning a family might want to consider the displacement implications.

The 125 requiring secondary education again equates to 20 in each of the school years. Some will qualify for a Bucks grammar school place, but the majority (perhaps 90 or so) would gravitate to the local Community College. Except that the school's roll is full and, (based on intake from the existing community), is expected to remain so for at least 5 years. Tricky one.

To sum up: Looking at schools highlights the size of the NSE's housing development - the displacement of local children in local schools ripples upwards and outwards throughout the community to affect all aspects of village/community life.

Services
Q.   How would doctors, dentists etc. cope with an extra 850 people on their books?
A.   Badly! (Particularly in the short term).

There are two surgeries serving Chalfont St. Peter. sense understands that the Misbourne surgery is near to closing its list whilst the Calcot surgery is, to all intents, already full. Could they not take on an extra doctor or two? Well, that's not really the problem - the surgeries are of a certain size to meet expected demand - it would not be trivial for them to extend their buildings to provide further consulting rooms/waiting areas to cater for an influx of 850+ people. They may well experience particular problems in addressing healthcare needs of the elderly in the residential home and sheltered accommodation.

Other services would probably be strained in the near term but able to adapt over time and then cope reasonably well.