If I call SetRowHeight or SetColWidth after I have changed the standard font, the row height/column width is not stored correct. If I redraw the grid, and then call SetRowHeight everything works fine.

You have to call

UpdateFontMetrics();

after you change the standard font.

The reason why it works fine after redrawing the grid is that in the grid draw method, UpdateFontMetrics() will be automatically be called.