Is there any family history which has led you to be looking out for signs of Neurodiversity?
Lots of the things that you are concerned about would be typical for a nearly 3 year old. Repetitive play is often evident at this age. Echolalia can be a feature of language until around 3 years of age. Please do not discourage this. In children who are ND this can be a stepping stone to developing spoken language ( I’m not suggesting that he is)
Children learn language from those around them so he will pick up words and phrases from you.
Children who are ND usually have a very uneven developmental profile. You say he met most of his milestones.
Most of your concerns seem to be around language development or use. Does he attend a Preschool setting and if so have they expressed any concerns about social communication and interaction difficulties? From what you have outlined it doesn’t sound like he would meet the threshold for a SALT referral.
You don’t mention any sensory differences e.g. avoiding or seeking certain textures or movement, avoiding some clothes textures or rigid or restricted diet?
I understand that you are anxious and that’s why you have asked for opinions. Every child is different and without knowing or seeing him ( even with experience or qualifications) people on MN can’t really say.
Our daughter at this age, although clearly demonstrating high ability, had lots of sensory needs, receptive and expressive language difficulties, restricted diet and sensory needs. She was diagnosed with SPD and then ASD age 3 1/2.
It does sound as if you are assessing and observing him. For now I’d try to enjoy playing, sharing books etc. I’m sure staff at Preschool or school will let you know if they have any concerns.