C.C.
Just my opinion, but if you have a child who is easily overwhelmed and a bit shy, you will be better off planning something small (like 2 or 3 friends, or even cousins or siblings if he has any). My younger daughter was easily overwhelmed at that age, so we made pizza (an activity she loves) at home with her big sister and a cousin. She had a great time and did not melt down. We wore party hats and had cake when we were done eating pizza, and then the kiddos went off to the playroom to play for a while. It was low-key, but still a celebration, and she made it through without any meltdowns, which was the priority for us.