M.P.
I suggest that it will just take time for both of you to get used to this new situation. You set limits so I don't understand why you'd need to set more. Or did you let him play with the neighbors?
His total meltdown is understandable. He's in a new house, in a new neighborhood, in a new school. He was tired out at the end of the day. So reasonable that you don't let him play with the neighbors. He may very well have had the meltdown even if there were no kids to want to play with.
I suggest you're being too hard on yourself. Give both of you time to find the right balance for you.