umbdude

There isn't a UWorld-equivalent. The ANCC board exam is nothing like the NCLEX and there isn't any good exam prep. The ANCC question bank (the one with ~100 questions) is the closest to the questioning style in the ANCC board but because there're only 100 questions, it's not a good source for review. The purple book and class notes should suffice for review.
I also used Boardvitals, which is close to UWorld in terms of difficulty and it's a great learning tool for yourself, but it's not very useful for the ANCC exam prep because the questions are nothing like those on the exam.

It is possible. However, the demand for psych NPs to do a lot of therapy is minimal at best. You will likely have to create your own path by working in a private practice that is willing to accommodate your interests or go solo. My guess is that your income will reflect that of a therapist, not a typical PMHNP. However, some therapists do make very good money in private practice. But those therapists generally have advanced psychotherapy training such as PsyD, clinical psychology, or to a lesser extent, LCSW.
Just my two cents...the psych NP path really does not make sense if your interest lies primarily in psychotherapy. We're trained almost exclusively in the biomedical/nursing model, from A&P in pre-reqs to psychopharm and diagnostics in medically complex patients during PMHNP program. Graduating from a psych NP Program doesn't mean you'll be an expert, and that learning will go on. If your interest isn't in psychopharm and medical science, your knowledge base could fall behind rapidly.
But the most crucial issue is that the psychotherapy training in a psych NP Program is extremely limited. You will likely put in a lot of additional time and money to get certifications after graduation. It'll probably take years to feel the level of competence that a PsyD or LCSW have. 

I think $75-$100k for a Duke NP degree is worth it. Most decent and nationally-known NP program will cost $60k+ anyways (excluding state schools). Anything beyond $100k for a MSN-NP degree is way too much though.
I've found that grad school professors treat students with more respect. Top programs usually have very supportive faculty and staff.