I didn't know DD was autistic for certain until the teen years and she found Primary fairly easy. The Ed psych said that her ability had masked her disability.
However even though she didn't have a diagnosis (and how fab you have things in place already and the staff can accommodate him) she started school with all sorts of skills at home, was already reading etc etc, and at her first parents evening I was told she didn't really play with the others and just liked to watch them and when I mentioned that at home she was already reading they said that if that was the case she wasn't showing them what she could do at school. In hindsight these were the first real clues, she wasn't showing them what she could do because they were using books with no words to describe the pictures - she still struggles with that now in her teens and she is a top achiever in all her classes. It took her a good 9 months or so to settle I think until she was really doing her academic best and then she flew and hasn't stopped.
In terms of friends she has always since Nursery had one really close friend, for well over a decade that friend tends to hunt and gathers others to mix in their circle and those others come and go.
DD was also involved in groups outside of school where she made friends, if you can find some groups that attract the more ND like Lego, or similar then he can develop friendships whilst doing a more calming activity, libraries are great for finding these groups and then you can use that for your bday party pool too.
As for following instructions DD has always been a rule follower, and if there ist a rule but she thinks there should be she'll make one so had no issues on that front BUT she was very, very worried about the idea of breaking a rule.
In terms of birthday parties my DD got invited but actually always found them quite overwhelming if they were the bouncy castle and disco type, she preferred an activity, same for playdates didn't like people in our house so I'd take her closer friend out for the day with us, parties at activity venues and now she's much older we hire a Haven caravan out of season as we live on the coast and take her friends for the full weekend as we don't/can't host at ours.