My grandson is on the autism spectrum and I've done a lot of reading as well as going with him to evaluations and therapy. Nothing that you said in this post sounds like spectrum issues to me. Aggression can be caused by so many things including lack of teaching about feelings and how to handle them in non-aggressive ways as well as a difficult invironment. Picky eaters abound without an autism diagnosis among normal children.
What did his OT therapist suggest? Because he's improved with OT in a short time, I suggest he may be having or have had sensory issues that can also be unrelated to autism.
I suggest you get an evaluation directly from a professional person/persons. The school district is mandated by Federal law to provide such evaluation free and then, if needed provide treatment. Call the school district office and ask for the phone number for the office that handles such things. In Oregon the office is called (county) Intermediate Education Service District.
With my grandson we also eventually learned about seeing a developmental pediatrician. We wish we'd known about that route in the beginning. This service is covered by my grandson's health insurance. The pediatrician acts as a coordinator and therapist. She made referrals for OT evaluation and treatment as well as speech therapy. My grandson gets services from both the school district and via is health insurance.
My grandson, now 9, was eventually and recently diagnosed with Aspergers. The system was hesitant to give a definite diagnosis until he'd been in treatment for a couple or more years. He, too, is outgoing. The difference is that he's unable to pick up on social clues and is awkward. This does result in anger much of the time. This wasn't so apparent until he was older and still doing the same inappropriate things as he'd done when he was younger.
A 4 yo is expected to be socially immature. What counts is if he's learning with experiences.
Later: Did you choose to remove him from the schools or did they ask you to remove him? If they didn't ask you to remove him I suggest that you were premature in removing him. The school staff will continue to work with him, helping him to learn how to get along with other children. He gets along well at home. Now it's time for him to learn how to get along in preschool. Many children are aggressive. Staff is trained to help them learn how to manage their feelings and get along with other children. It's a process that you may have stopped too soon.
Since your pediatrician suggested, in an earlier post, that your son is not "all that bad" I wonder if you're too sensitive, wanting your son to get along automatically without going thru the learning process. Are you expecting a certain behavior that your son may not have learned yet? Have you given him and the school the time for teaching him?
Perhaps he's not yet ready for preschool, in which case keeping him at home is the way to go. However, at the same time, you don't need to feel that he's handicapped in some way. Kids all mature at different times.
I'd stop looking for something to be wrong and enjoy him as he is. Perhaps get a professional evaluation so that you'll feel more comfortable but stop googling possible behaviors.
After your SWH: You took him out of school because they suggested you contact Special Ed.?? even tho you too were concerned. And now you're involved with Special Ed to get an evaluation. Special Ed does not mean mental retardation or whatever the pc term is now days. Is that why you took him out of school? Special Ed provides help for children who have special needs which includes mental issues but also such things as autism, sensory processing, speech delay, etc. Sounds like you're thinking that Special Ed means autism. It does not.
It is thru the Special Ed department that evaluations are arranged. I'm glad that you're doing that.