A point that doesn't seem to be mentioned is what is the effect on current services having to serve two new stations. How many train paths do they take up. It should be remember that both Cullompton and Welling had 2 through lines with their platforms on loops allowing slow trains to be overtaken by faster services. perhps they should be provided with a bidirectional line speed through line to allow overtaking.
Another issue as has been mentioned is how do people get to the station, as has been said public ransport needs to be ready before the houses are occupied.
Further if we going all electric how many charging ppoints will be provided in the carpark? How would they be allocated it would be unfair if the first people there plugged in and remained plugged in all day denying others the chance to recharge perhaps we'll need carpark "shufflers" to move cars around.
On the last point, I would suggest not having any charging points at all. The worst performing electric car would manage a 5-mile radius there and back journey for a commuter catching a train to work every weekday for a fortnight on a single charge at home. It might sound heretical, but we don't have a petrol pump at every station.
For the middle point, a regular bus service from the growing suburbs through Wellington would be lovely but unlikely without some pump priming money. Failing that, the 22/22a stops there half hourly at peak periods.
As for the first point - that will take a substantial slice of the £5 million to work out, and if it comes to the conclusion that loops are needed, that will be the end of the story.