Since you're interested in psych NP, taking psychology classes is essential. I went back to do a second degree in psych and am very glad for it. You should aim for a minor in psych if you can, or a major, in addition to taking science classes (anatomy, nutrition, microbio, organic chem). You should also try to get research experience in psych by volunteering your time as a research assistant. I worked in two labs and found it to be quite valuable. One of them I got lots of experience doing diagnostic assessments/suicidal risk assessments. Try to find a professor doing research in something you find interesting and relevant, preferably clinical psychology/psychiatry.
Also you should try to volunteer in psych ward in a hospital or an outpatient mental health clinic. Do this for some time (at least a year) and form a relationship with a psychologist, psych NP, or psychiatrist who will then write you a good letter. Do the same for your research supervisor (a professor, not a grad student). Those 2 letters of rec will go a long way. The 3rd, if needed, can come from a nursing professor who you should have taken more than one class with (and actually spoken to outside of class so that they know who you are). Do all this while keeping a 3.4+ GPA and you will be very competitive for NP school. Also, kill the GRE. It's easy. PM me if you want study tips.
One thing though, you said you want to do 75% counseling and 25% medication management. I am not a psych NP yet, but from what I have heard, psych NPs do not really do much counseling. It is mostly medication management with very minimal counseling, if any. The only way to do psychotherapy as a psych NP is to have a private practice, which is certainly possible. That's my goal actually.