Wilson's doesn't have school buses. The boys use public transport.
Have a look at the school websites to see the catchment areas for the girls' schools. By three schools, do you mean Tiffin Girls and the two in Sutton? Tiffin Girls would be quite a trek from Wallington/Croydon.
We don't know your son and whether the school would suit him. Did you go to the Open Evening?
I have two sons at Wilson's and it's a lovely, happy school. There is a big emphasis on doing extra curricular activities - music, sport, CCF mostly. The boys are expected to try hard and there are high expectations on behaviour, but there are a few annoying, poorly behaved boys. My sons have made lots of friends, but there isn't a lot of going to each other's houses, because the boys come from such a wide area.