I don't think you need to worry so much. This is all normal.
My only other suggestion would be to read prior posts about this..I've answered some of them too.
Get him his own "baby" to take care of. Stock the house with BIG BOY toys and activities that only come out when the baby is napping so he gets some attention too. The big boy toys go away when you leave to fetch the baby - tell him to clean them up so the baby doesn't get them. Make sure that all people coming over greet HIM before they see the baby. And when others are holding/visiting the baby, give him a craft, coloring, etc to do so he doesn't feel left out.
Also, get your husband involved. You are going to need some rest and down time. Try to get Daddy to help NOW with after dinner activities like cleaning up with the Big Boy, taking a bath, reading stories and putting him to bed. That way it won't be such a culture shock when mom is busy taking care of a newborn. Daddy should have his Little Buddy be Mommy's Big Helper. Have Dad ask everyday when he gets home - did you help Mommy? Did you listen good? Etc.
Finally remind your Big Boy that he gets to do things/have things that babies don't. Although a regression is normal during this time - like having potty trainging accidents, waking at night, talking babish, etc. He should understand that Big Boys get to stay up later, eat ice cream/fruit snacks, etc.
Finally, one "trick" I learned was tell the baby to wait for his/her turn. As in, when the baby starts fussing, tell the baby, "Now Susie, you need to wait your turn. I'm helping your brother right now with his lunch." Of course the baby doesn't understand, but the Big Boy does. First, that we each have to share Mommy's time and attention. Second, that sometimes HE comes first too.
Best wishes. And try not to worry about this. Get Daddy to start being your Big Boy's buddy and everyone will do just fine.
PS. We had a gift for our Big Girl when she came to the hospitial. We told her that her little sister had a present for her. She LOVED that.