You need more than 1 paint window open to make a collage like that, have one window just for pasting and cropping, and the other one for sticking them all in one image
Also to make it update, there used to be a photobucket method where you could edit the image through photobucket's editor and have it update, but I'm not sure that works anymore
You could try using an image rotator (like grumpybumpers) and just replace the image link every time after editing it and crossing out items