You don't want an A7, the camera must have on-sensor PDAF points. This means at least an A7-II, later models have more PDAF points across a larger percentage of the view.
To answer your question, controlling the camera AF via the remoteapp should work fine with the Techart adapter.
The touch screen on the smartphone can be used to choose the focus point, it shouldn't matter if it's a native E mount lens with autofocus or a lens on an AF adapter.
I have tested this with an A7-II using a Fringer AF adapter and Contax N lenses, works fine.