Intake valves pass only air or air-fuel mixture so they run at much lower temperatures than exhaust valves.
They are usually larger than exhaust valves because the pressure forcing the charge into the cylinder is much lower than the pressure forcing the exhaust gases out of the cylinder. Exhaust gases under pressure need much less space.
Different engines use different valve combinations.
Having more than 1 inlet valve provides better breathing. An additional inlet valve allows larger inlet passages and a freer flow into the cylinder, so the engine receives a better charge.
Similarly, two exhaust valves mean the cylinder can be designed with larger exhaust ports, which provides a freer flow of exhaust gases out of the cylinder.
