If barriers are going to be placed at all N.R. stations, what is going
to happen at stations, like Wandsworth Town, where the ticket office is
on the island platform, on the trainside of any likely barrier
position?

No one has said everywhere is getting gated. Validation equipment is
required and it will be to the same design as used on some NR stations
north of Queens Park or on the DLR.

You still need a local network to provide the necessary info to and from
the devices and to support whatever retailing infrastructure is going to
be provided.

I'm just pleased to see some sort of progress at last. I'm curious to
know what strong arm tactics have been employed to get this deal
through.

According to a report on BBC London News the TOCs are not happy as they
were not consulted about the TfL/DfT deal.