Hey IE, I've noticed that you edit some pages multiple times to add categories. It is possible to add multiple categories in one go by editing the page, or using the category field available when viewing the page as well. It's not necessary to do each one separately.
It doesn't have to be a specific size, you can try .jpg files as they're much smaller than .png files. If you have any kind of photo editing software try cropping the part of the image you want and saving it as a .jpg
I don't know how to search for picture size, sorry.