6 y.o with bipolar/adhd/behavior/anxiety issues denied iep but is he eligable?

My son whom is six years old entered kindergarten this fall. In March I requested an IEP for him. They did the testing and found him not eligable because he had no sigificant delays. He gets SSI for his bipolar disorder. I came home and researched, advocated for him and got him covered under Section 504 so he does have a 504 plan in place for him at school which includes a 1:1 aide, counselling, social skills group, bahavioral ysis, and behavioral intervention plan. I just got him a neuropsych evaluation on my own. The dr. said that my son needs an IEP, along with smaller cl size preferably no more than nine kids and two teachers. He believes that my son has ADHD, and bipolar with rapid cycling, along with some other diagnosis that he is not sure of yet without the results being scored. He is going to have me a preliminary report for our 504 plan meeting next week. He told me that if the school denies my son an IEP again, for me to get a lawyer. My son gets anxiety from being with all the other children, has had behavioral problems at school in the last couple weeks including hitting another child, kicking a girl, hitting a teacher, biting the sped director bloody, hiding under the structures outside, slamming lockers, and sleeping in cl. Do you agree that with these behaviors his education is effected by his disability and that he needs an IEP? Also does the school need to abide by what the neuropsych director recommends?"