yeah it think it is outline first because its a window so its clear meaning if you do the fill first then the outline you would only be able to see it from the inside due to the way it would layer. So im guessing you would have to do the outline first then add any highlights / details that would be in the fill like dots stars lines ect then do the fill. no matter what your fill would have to be last.
But ive never tried it i just used a little mind power.
Oh yea and im sure if you are doing a simple straight letter like in that first pic it youldnt really matter which one you did first but in the second and last pics it should be how i said.