Yes, I think everyone needs a mentor. It's hard to find someone who knows everything and has all the answers but there are always people around us who can help us in different areas of life.
I don't think so. There are people who prefer self-taught, they may be comfortable in this way. Not every sector in life requires mentors, there are some matters that we can learn ourselves. Even for trading and investing in crypto, there are also people who do it by self-taught. I also learn crypto myself, I don't have any mentor so far. 
Mentors accelerate growth, but self-driven curiosity and resilience often define success. Is it the teacher who makes the student, or the student who chooses to learn?
Ideally, mentors only function to guide you. You must have your own intention to learn. If you have no intention to learn and to succeed, mentors can't do anything. Your intention will determine how serious you will make efforts.