There is no need that all movements are done on the same time. You can pinch by moving one edge and then after this moving the other edge.
The pan is a translation. It doesn't need any center of transformation. It is a transformation that is done only by swiping on the n900, without any change of mode.
You can't paint on a multitouch device at all. The fingers are to thick. You can only do the drawing of a 4 year old child. And if you do serious painting you don't zoom, pan and draw at the same time. An intelligent person does one thing after the other one. If you do everything at the same time everything will be bad.