It depends on each situation. Tough to answer well without the context. But that said, generally:
3 because it's the proof that users give you
4 to amplify #3
1 to further explain your message to new audiences and it can sandwiched before and after #4
2 you need to have a really polished product for them, or they will kill you initially. startups doing business with the big companies is not an easy task.