Pervasive Development Disorder places someone directly on the Autism Spectrum. PDD means Autism Spectrum Disorder (ASD) whether the NOS is added or not. Most people with Autisms are very intelligent and can be very verbal.
ADD/ADHD is often diagnosed along with ASD if there are attention and concentration/focusing problems particularly in the classroom. In your son's case the ADHD would be part of the Autism and not separate from it.
If he's covering his ears and is sensitive to other sensory stimuli (textures for food, tastes, smells, touch, etc) he sounds like he may possibly have Sensory Processing or Integration Disorder (same disorder, different name). This is part of the Autism and not separate from it. Self injury would be part of this as well. Self injury can be used as a distraction from something that's overly exciting or upsetting... but it is very often something called Sensory Seeking Behavior and it's to satisfy a need for sensory input. When I realized this with my middle daughter, I started her on what we call a Sensory Diet.
With a Sensory Diet we give her things every day to stimulate her senses. Sometimes it's tickles up and down her arm. Back rubs. Brushing her hair. Head rubs. Letting her play in sand (she loves her sand table) or dried beans or uncooked rice. Letting her play with Play-Doh. Letting her play in a sink full of water with some toys. Setting up a bucket with "slimy" cornstarch which is just cornstarch with enough water added to make it similar to "slime" like on TV. :-) She also will get a little cup out and drink lemon juice or she'll put red hot sauce on bread or corn or chicken.
Anxiety Disorders are also often part and parcel of Autism. So is OCD aka Obsessive Compulsive Disorder, and so is ODD aka Oppositional Defiant Disorder.
Staring into space may be a sign that he's trying to process or detox something he's experienced, however with my daughter it was a sign that she was experiencing mild seizures so please have your son see a Pediatric Neurologist that specializes in Autism and other Behavioral Disorders. Things like migraines and seizure disorders are 75% more likely in people with Autisms.
He may make animal noises just because he likes them. :-) If he has a lot of repetitive behaviors or words or phrases or sounds, those have a function and they're called Perseveration. They are Perseverative Behaviors. We all do them to some extent but they're more noticeable with people who have ASD. Arm flapping, repeating a word or phrase someone else just said, repeating the same thing over and over and over, jumping, hopping, spinning, rocking, running in circles, tapping, humming... all of these things. And there's a function to them which a lot of research seems to suggest is that it's all soothing and can even help them focus.
I know that this is a lot... and there's so much more. I'm not so sure that your son has a psychosis... he would need a Child Psychiatrist to evaluate him for that and to work hand in hand with a Child Neurologist as well. I know how difficult this is and can be... I have an ASD child too and while it looks bleak, remember that he's still the same little boy you've always had. NO ONE is saying that he's not smart or sweet or perfect. Okay? Autism doesn't take those things away from you.
What happens next is that you ask the school for a formal Triennial Evaluation so that your son can get Special Services from school. The evaluation will determine which target areas he needs help with and the school MUST perform this test on their own dime. It's a federal law. Your son is entitled to an appropriate education that fits him specifically, so he should have something called a PPT (Planning and Placement Team) with the school that you will be a part of to formulate an IEP (Individualized Education Plan) for your son.
You'll get through this, I promise you. Just remember that this is all connected. If you want to try to minimize some behaviors, you can try tweaking his diet a bit and reduce or eliminate high fructose corn syrup and artificial food dyes such as Red 40, blue, green and yellow. The worst culprit is Red 40 and HFCS. Children with ASD seem to be particularly sensitive to these chemicals and can make their symptoms worse.
EDITED TO ADD: What MelissaT is talking about is NOT AUTISM. She's talking about vitamin deficiencies and food sensitivities that present as and mimic Autism and other Neurological Disorders and Behavioral Disorders. If a child has a Gluten Intolerance or Dairy Intolerance, or is sensitive to HFCS, sugar, and other foods and they completely eliminate trigger foods from their diet and turn into completely typical children with zero symptoms of Autism or any other disorder, then it was never Autism to begin with. If the behaviors decrease but don't disappear even with the dietary accommodations, then keep up with the dietary accommodations but that would mean that the disorder isn't as severe as originally believed.