WillAdams
(William Adams (Carbide 3D))
2
Where the cutter will be placed in relation to the path is a function of two things:

the diameter of the cutter — this will determine how much the offset (if any) will be — note that you may want to do a test cut in a scrap of material and measure that first: Shapeoko CNC Router, Rigid, Accurate, Reliable, and Affordable

the toolpath selected, which will determine whether there is:

Contour  Pocket or Inside / Left — the toolpath will come no closer than 1/2 endmill diameter to the geometry from the inside

Contour  Outside / Right — the toolpath will come no closer than 1/2 endmill diameter to the geometry from the outside

Contour  No Offset — the toolpath will follow the geometry as precisely as machine motion allows
Play around with assigning toolpaths — you’ll get a preview image of the toolpath after assigning it which will help to show that.
There’s some discussion of this in: