Rob
Ansys Employee

If you click on Help most of the settings will be explained.  I generally leave the tolerance alone, looking at your result it's fractionally altered one-two pathline trajectories such that they've entered a recirculation zone. 

Which surface? I can't answer that. I use inlet, reverse from outlet, labelled interior zones and (on occasion) rakes. Post processing is the part of CFD where you get information to explain the result. So, there isn't one answer. A mix of pathlines, vectors and contours will cover most applications, possibly with some numerical data (pressure loss, mass flow, residence time) as needed.