@HeckyPeck
If she had come on here and said 'how can I prevent my four year old DSS from poking my newborn' she would have had different answers.
She seems to resent this poor child for existing.
Imagine complaining she only had two weeks without him to 'bond'. Hes part of the family, exactly how long does she think he should have been banished for?
OP, I have a newborn and a four year old, among other children.
This is early days, four year old is excited and adjusting and figuring out the new world order. He won't always be this intense about the baby. Likewise, the baby will be getting stronger and bigger every day and you will be less worried about something going wrong. You will also see their relationship develop, your baby's face lighting up when his or her 'big' four year old brother pays attention to them. You'll see the wonderful parts of having a sibling soon, and that will balance out the stressful part.
Some tips - your four year old is probably hearing a world of 'no' at the moment and not mature enough to understand why. So try not to say no.
Re poking: 'baby loves it when you gently stroke her with the back of your hand, can I show you? That's right! Oh look how happy and calm she is'
Re breastfeeding: Timmy, I'm going to feed baby. Can you use these blocks to build a big tower for her to look at while I burp her? She'll be so impressed, she's too little to make a tower.
Nursery germs are part of the deal. The alternative would be to keep him home with you while you're on maternity leave- so consider whether that is appealing to you. I had to do that for medical reasons and with my previous child and it's doable but hard. You can encourage hand washing, and sleeve coughing and at four he is old enough to understand that he needs to keep his face away from the baby's face when he has a cold, so include him in that without saying 'no' too much. 'Timmy we don't want germs to spread to baby, so while you're sick let's just kiss her feet.'
Nappy changing etc- anticipate that he wants to be involved, instead of getting annoyed- include him, give him a little job to do. 'Timmy, can you please choose a nappy? Timmy can you sing a song to baby to keep her happy while I change her nappy?'
He'll learn to be more gentle.
But you need to be kinder to this poor kid, your post was really hard reading and I think if you read it back in a couple of years you'll feel mortified that you were so hard on him.