Ceramics are more commonly used in bathrooms and on walls as they are not as dense as porcelain. Porcelain is fired in the kilns when produced to a higher tempreture therefore perfect for high traffic areas.

Short answer no, ceramic wall tiles are not strong enough to be used on the wall, but you can use a floor tile on the wall.

No, quite the oposite using small tiles in a small area creates more grout lines and therefore can draw the area in making it look smaller, using a larger popular size like a 300x600mm will give you less grout lines making the area look bigger.