I'm a high functioning autistic 33 year old and I can share some of my own experience. The meaning of this post is not to be immediately applicable but more to widen your scope of autism as a whole. Most people are surprised when I tell them I'm autistic, but when people know what to look for they say "I have all the symptoms" which is not 100% accurate.

Most of my social skills I had to learn manually. I felt like I was falling behind socially at age 9 but somehow managed by getting one friend that was always up for playing video games. I recommend explaining in detail facial expressions early, learn how to read body language and then explain it to him.

I'm not sure where I stand on video games since it took me a long time to be able to play in moderation.

Structured activities are the best. Playing board games is really fun and easy way to engage socially with other people(monopoly is really bad, get Catan or other modern games instead). This is why individual sports are very calming such as swimming and athletics suit very well when teamwork could cause friction. Chess is also a nice sport to get into.

One thing you don't want your child to do is to end up masking, "acting normal" takes a ton of energy where you have to be constantly alert of every minor detail in yourself and others since it's not automatic. Focusing on other people only saves a lot of energy, focusing on a single other person is a "solvable problem".

Another thing you should check for is whether you or your partner yourselves have autism. Contrary to popular belief you yourself are very qualified of judging yourself. Be careful though since wording of many tests is written by non-autistic people so answering "I'm not bothered by things that interrupt me from pursuing my major interests." and thinking "Not really, I have a system for that" is not the way they intended for the question to be interpreted.

I had trouble expressing myself growing up until I gained sufficient vocabulary to be able to precisely say what I'm experiencing. Rather than make attempts I stayed silent but giving me time, paper and pen would have helped. I think this issue might stem from me saying something, it being misinterpreted, and then the conversation spinning off in a completely "chaotic" direction.

I have a friend now that's same age that when I say something in a group nobody gets it and he "translates" for me. I suspect he's also autistic.

Autistic people not wanting to speak is not true in most cases. Often in a group it's just impossible to keep up. However one on one many of us can talk for hours about a specific interest.

I'll leave it at that and with a quote from a parenting book. It was aimed at conversation between the parents but it very much applies here also. "What's obvious to you is obvious to you." There is an ocean of things that are obvious to non-autistic people that need explaining. My wife and I frequently have something to like "It's in the bag." In her mind it's "The bag we have been using all day" in my mind it's "The most frequent bag, the grocery bag, the bag she was using, her purse bag and the regular storage bag are all candidates". She's since started saying "The blue bag that's on the counter" instead which makes everything crystal clear in seconds.