3. How do I monitor the accommodations process to ensure it's working?
I would pay someone, maybe whoever did your neuropsych, to do an observation. In our case, the school really did very little in the 504 plan.
Thing about 504 plans is that you get accommodations when they are needed - like for testing or extra time for homework/assignments. So, you could send someone to observe, but if it's a day where no accommodations would be needed, then you aren't going to see anything. Also, if the accommodation is extra time, often it is given on a later day after the assignment/test is reviewed to see if extra time is needed.
I monitor through talking with my son, reviewing Edline and, when I have questions, talking with the special education team and teachers. I look at outcomes - if my son got the grade I expect based on his abilities. I haven't had a negative experience with special ed in MCPS, so I don't come to this process with a mistrustful attitude. What I find is that everyone is invested in my son's success and they really to work hard for him.