Wheels dont make a skateboard easier to turn on the skateboard trucks do that.
Plastic? Ive never seen metal wheels
A kick turn is when you turn not by leaning to the side, but by lifting your front wheels and moving them in a different direction to turn.
yes the sizes of skateboard wheels range from 40-70 mm
This is a mighty vague question, but I'll give it a shoot. A skateboard has wheels - when these wheels are acted upon by a force (such as you pushing it), they proceed to take the energy from that force and change it into centrifugal and centripetal forces- this causes the wheels on your skateboard to turn. Your skateboard won't roll indefinitely from 1 push because while your skateboard is rolling it is creating friction with the sidewalk you're skateboarding on. Friction is caused when 2 objects rub up against each other - this creates heat and a transfer of kinetic energy. Once all the kinetic energy has been transferred from your skateboard's wheels to the sidewalk, your skateboard come to a stop.
Bigger wheels make it easier to roll over cracks in the road. softer wheels are good for riding vert because they grip the ground alot better than hard wheels.