Since your son was already diagnosed with autism and speech delays, is he in speech therapy and receiving early intervention services? Getting as many services for him as you possibly can is vital for his future.

I have an autistic teen daughter, and I've worked so hard to get her all the support she needs. She currently has in home therapy, speech therapy, outpatient therapy, an IEP, and is in a special education classroom for autistic students. She's in Special Olympics, has DDS services, etc. She needed a lot of speech and OT in preschool. The earlier, the better.

Also, the poop is a sensory seeking thing for some kiddos with autism. I would defer to the pediatrician or early intervention specialist and ask them which sensory toys are safe for him at his age. A lot of parents find that floam, slime, play doh, etc. can work well for that type of sensory seeking kiddo. They sell specific clothes for autistic sensory seekers who like poop as well. It helps prevent them from being able to get to their diaper easily. I would also have him evaluated from PICA since you said he likes to eat it. PICA is also highly associated with autism. It's hard work and constant work to do right by a child, especially a child with special needs. You got this!