On Reply, there's a "Go Advanced" button that lets you upload images.

Mostly, I'm looking for a description of the resolution of your PNG (pixels wide and high) and approximate size and placement of land masses (you have that here). The attached tutorial makes a few assumptions in that regard.

Make sure that you don't confuse the "planar world" and "flat world" items in the new world wizard. The planar world is exactly that: a flat plane for which the notion of "projection" is meaningless. The flat world is a spherical one that starts out at 0 altitude everywhere (it sets worldwide editing roughness to 0, if I recall correctly). This spherical world can be viewed in many projections and all are equally valid. The equirectangular projection is a special case projection of a sphere with a simple n:m angle (latitude, longitude):pixel relationship; the planar world is a literal flat area with a n:m linear distance:pixel relationship.

FT From Contours.pdf