Dark matter consists of galaxies, stars other matter that exists in the universe
Dark energy is the energy exposed by dark matter. It consists gravity too
Yes neutrinos have mass because it's subatomic particles produced by radioactive decay
Universe had begun by big bang
A explosive matter that had started the concept time and due to the big bang explosion universe had became visible
Protons are unstable because it has positively charged ions and we know that an ion doesn't consist in neutral phase that's why protons are unstable in nature
Yes, there is new state of matter called plasma. It is mostly charged by protons and electrons. It is invisible state of matter. Plasma matter consists more in the universe. At least 99% of universe is in plasma state.
The concept cosmic event called big bang which had started time and made universe visible can be studied through big bang theory