- The "wind" is composed by electrons and ions (1 proton from Hydrogen and 1 proton and 1 neutron from Hellium). The speed is measured by watching a solar flare and measuring the interval it takes to reach a man-made satellite specially designed for measuring Sun radiation reaching Earth, by balloons with instruments, by planes with instruments and on land based labs. The speed varies greatly upon the intensity of the flare.

- Protons and electrons, don't forget that. Google the answer.

- Insignificant amount of mass. Total mass of the Sun is about 2.67Exp27 kg. The mass of a proton is 1.67Exp-27 and the number of atoms in the Sun is about 10Exp54.
The solar wind particles take between two to four days to reach earth, so do the math of the speed. There are about 300 million protons per square centimeter per second at the Earth’s distance from the Sun. Once again, do the math regarding an sphere with a radius of 150 million Km, and you`ll have your answer.

Google it.