question about column grid properties palette
The insertion point is just the reference for initial placement. It still exists afterwards (you can use the INSertion Object Snap to reference it, but it has no real effect on the function of the column grid.
I am not clear on the second part of your question. Are you referring to the Layer property on the Design tab of the Properties palette? The only choices on that drop-down are to set the layer on which the Column Grid resides. Or are you referring to the properties of a Column Grid tool palette tool, under the BASIC category, under the General subcategory? The Layer key and Layer override properties there do not have a drop-down menu, but instead open a "worksheet" dialog for choosing the value desired. The Layer key property allows you to choose a Layer Key other than the default GRIDLINE and the Layer override allows you to override the values of selected layer name Descriptive Fields, if your Layer Key Style uses a Layer Standard that has Descriptive Fields defined.
Layers provide a means of organizing the various objects in a drawing. The layers shown are based on the US National CAD Standard, which breaks up a layer name into a number of fields. The first is for the discipline and is at least one character in length, but may have an optional second character; "S" designates structural. The second field is called "Major", is four characters long, and represents major sections of objects under that discipline. "Cols" designates columns and "Grid" designates grid (for structural, column grid).
Optionally, additional four-character minor fields may be added, to subdivide the objects that fall into the major category into subcategories. A final, single character status field, also optional, can be added to designate new work ("N"), existing-to-remain ("E"), existing-to-be-removed ("D"), etc.