On my mind:
1--I need the NP report so I know what is going on and what to do about it.
Yep.
2--I want to engage with advocacy agency but feel like NP report is important piece of that.
You can start on this now, by describing who he is and what has been happening to him. The NP information will inform this but you also have a lot of reasons why you need advocacy.
3--I would not "lawyer up" on the 504 issues because I don't think they were intentional. If the principal is unwilling to discuss a grade appeal in the art class, I think I will escalate to district admin--and that's where I might be willing to consult attorney. In this case, it is really the principle of the thing--that man actually, emotionally abused and damaged my son, retaliated against him (me?), and exercised "power over" in a truly disgusting way. At the very least, I want acknowledgement from the administration. I have mountains of documentation and none of it reflects well on the teacher. I would even consider suing the teacher for malpractice--I can't tell you how outside of my personal comfort zone that is but I want something about this situation to be just. I can't let an adult in a professional role abuse my son, get away with it, and just pretend it didn't happen. When I described the situation to my therapist, she said it was sadistic.
Yes. I would keep this on a tight timeline--if Principal doesn't respond to the paper letter, I'd be in contact with district, evidence in hand. If they decline to act, then advocate. Then lawyer. If it gets that far you should also be actively shopping for alternatives.
4--I would like to begin working on a(nother) letter requesting special ed eval but I need the NP report.
Nope. Get out From Emotions to Advocacy. You do not need a dx to support this. Instead of naming a dx, you need to name all the different things he struggles with, you can cite horrid things the teachers have said, and ask for the eval. Start the clock on this ASAP!
You can mention that you are pursuing private diagostic information that may inform their process. But start the clock.
5--I don't think we can get private speech/language services in my city. I think he needs his pragmatic language ability evaluated. My spec ed friend said that "pragmatics are the hot new trend" and that if he is evaluated via school they will "take a look at that."
Much depends on the capabilities of the school SLP who evaluates. We have seen good and bad.
I want a referral and will travel where I need to but we need HELP (i.e. NP report).
I would ask a lot of questions of the NP in that meeting-- what therapies are likely to be maximally useful to DS? Who locally has the expertise to provide them? Is there help paying for them? Does NP know an advocate who can help? In short, pick their brain not only about exactly what diagnostic results mean, but also about recommended next steps.
The NP's report should also include next steps framed (preferably: insisted upon) in a way that the school can use them. If it doesn't when you see it, ask for them to be included because they are your best tool for getting the IEP in place properly.