Hello Keith
Don't worry about asking questions, better to get the thing clear in
your head.
Espaliers are a great way to grow, especially against a wall. When you
plant the tree it wants to be about 9"/22cm away from the wall, just
take a rough measure, it does not have to be millimeter prescision.
The tree wants some room to breath. You can gain the distance by
fixing the training wires on long vine eyes. The wires arn't taking
weight, they are for training

As far as growing as a tree, I would use Charles Ross, as I have found
it to be a partial tip bearer. Forms pleanty of spurs, but does fruit
on the end of new wood.

For a tree could I suggest Spartan, from British Columbia. It is a red
apple which has its colour develops has a white bloom to it. As it
ripens this disappears - so you know when to pick. It produces a nice
sized apple, around 60mm diameter and is a good reliable cropper. I
grafted one two years ago and is growing as a cordon, but the tree the
wood came from is in Barnsley, on an allotment, grown as a tree and is
clean and fruitful.

Up here in the north, cox does not do well but Suntan and Sunset are
more reliable and not as demanding. They should fair similarlly for
you. (As you seem partial to cox like apples!)

Regards

Clifford