When the image is printed (and scaled up 400% in the process) will the high res image be printed at the highest resolution available?
It will be printed at its effective resolution after being scaled. In other words, when scaled to 400% its PPI will be one quarter of what it is currently. If you want 50 PPI at full size and are drawing at 25%, then you want the raster image to be 200 PPI at the 25% scale in which you are drawing.
JET