Quite a few local boys go to Halliford, the school bus goes from the Hampton Court Way, or you can pick up the train from Kingston - lots of boys including my neighbours do.
DS's prep is quite near Radnor, his school runs a bus this way in the mornings but the 281 bus runs from Surbiton to Twickenham, and he gets that home, with other boys who live this way. The buses are very frequent and fairly quick, it's not a bad journey if you're near a bus stop.
I have looked at the school buses for St Johns,Epsom and CLFS for DD at 13+, we are Long Ditton and they all seem to go from around the Shell Garage on the Hinchley Wood bypass very early, and come back quite late. It's not walkable to Surbiton so you would have to pick up or he could catch K9? to Surbiton. I've pretty much ruled these out because of this, and have resigned myself to boarding fees if DD wants to move. But, they are all really good schools.
The KCS bus runs through Ditton Hill (DS starts there next September). St Pauls/Colet Court also run a bus through Long Ditton and Surbiton. The Hampton bus also runs along Ditton Hill, but only stops at the top of the hill, one of the many reasons DS chose KCS.
There is a lot of choice and you will find other families in the area making similar journeys that you can share lifts with.
Everyone I know with children at Radnor is very happy with it, there is a huge amount of respect for the staff who have set it up from local preps etc. It may be a good option for you because being new its unproven, so less popular than the established schools, but long-term it will do very well. It is "boy heavy", by virtue of replacing a boys school and being opposite a girls school.
Racing Heart has given you a pretty good list, all I would add is I would bold and underline the "not conventional" for HCH.