My DS1 can be a bit shy. He settled in easier as we had him in Before and After School Care. Initially this was due to me working, I now have him in one day after school care as he likes it so much. He gets to meet kids on school grounds out of school hours and then that has gone onto forming friendships during school hours.
I too always worried about DS1 as he can get taken advantage of pretty easily. The school also have a buddy system, does Yasin's school have one of those? They get allocated a Senior student who they can go and ask for help, the school also have the buddy's and their little prep have lunch together one day a week. It worked well for the preps.
Sounds like from your last post he is settling well