grid resolution of wire and insulation
Short answers: neither, and no.
"Grid resolution" typically means the size of the grid cells. Depending on the context, it can be the smallest dimension of the smallest cell, or of an average cell, or of the cells in a region of interest, etc...
"max step size" and "geometry resolution" are specific to Sim4Life. These settings are used to create the grid. I encourage you to read the relevant sections of the user manual to understand what these settings do.