On characteristic of a social justice counselor is being a courageous risk-taker. How courageous do you consider yourself to be when faced with opposition from others? Do you think of yourself as a risk-taker? What can you do to prepare yourself to be a social justice advocate for your clients?

Most of the questions that you pose are personal and can only be answered based on your assessment of your own character, work, and educational experience, and goals.
A good counselor is empathetic and, when confronted with opposition, tries to find common ground or mediates in the interest of averting further conflict. Think about your past experiences, preferably your work experiences, how have you worked to seek common ground or to empathize with colleagues when they expressed views that strongly differed from your own? Are you a good listener? Are you capable of empathizing even with people who you do not like very much? When people disagree with you, are you capable of not taking this personally and still respecting all points of view, including your own? It takes courage—that is, the ability to do things that may be emotionally and intellectually threatening—to be someone who can respond positively to all of these questions.
Similarly, I would encourage you to think of risk-taking in a similar context. Are you someone who is willing to hear, read, or engage with views that strongly counter your own? There is risk involved in this because you may find yourself challenged in ways that make you uncomfortable and that may even force you to reassess the views that you have always held dear and true.
In regard to preparation for being a social-justice counselor, I would encourage you to consult the expertly written articles whose links I have attached below. Regardless of your ethnic or racial background, gender, sexual orientation, etc., being a good social justice counselor requires you to try to think of all of the ways in which you may be privileged and to think of the experiences that often go undiscussed when talking about problems with mental or emotional health.
Legal scholar Kimberle Crenshaw, whose landmark 1989 essay about intersectionality is also worth consulting, has gotten all of us to think more about the ways in which privilege works across racial and gender lines. More contemporary dialogues have introduced language about ableism, sizeism, and discrimination against non-binary or non-gender conforming people.
When preparing to be a social justice counselor, it helps to think of the people who might normally be excluded or overlooked in conversations about mental health, as well as communities that tend to talk about mental illness as though it were a source of shame. Unfortunately, many communities of color do not talk openly about mental illness. This, in addition to the poverty that is also more common in some of these groups, makes it much harder for struggling people to find the health care that they need.
Furthermore, lingering prejudices plague other groups. LGBTQ people must still resist the prejudice of homophobic and transphobic people who treat their orientations like mental illnesses. A good social justice counselor is aware of these prejudices and, even if you have not dealt with these experiences, you would be prepared to provide some solutions for how a struggling person from one of these groups could get the care that they need and feel deserving of it.
https://ct.counseling.org/2016/01/multicultural-and-social-justice-counseling-competencies-practical-applications-in-counseling/

https://www.counseling.org/news/aca-blogs/aca-member-blogs/aca-member-blogs/2017/09/18/social-justice