Children don't want to be 'the boss', its frightening and makes them feel unsafe. Children do need boundaries to feel safe.
Yes, and that is why I suggested nipping that in the bud.
It can be done by insisting on 'please' and 'thank you', and by spending time together teaching the child something useful. Children of 5 and up love to feel they are helping, and nothing contributes more to a feeling of solid self esteem than working alongside a parent for reasonably short stretches. Giving them something to do all by themselves is too much though. While working, parent and child can chat. You could involve the child in preparing a meal, folding laundry, handing you clothes pegs, cleaning skirting boards, anything really..
Spending time together doing something you both enjoy, chatting together - even something simple like a meal everyone likes re-establishes a sense of connection.
It's important to reconnect and to reassure the child that you love him and you are glad you are friends again. A nice bedtime routine that is never affected by what happened during the day reassures the child. Try to tell yourself that tomorrow is a completely new day and don't dwell on what happened today/yesterday.
When a kid acts like this at this age, they know they're doing 'wrong' - but they literally can't help but act out. There are specific techniques and tools to get to the bottom of what's causing the dis-regulation, fix that and the behaviour goes away.
Naming the feelings, teaching self calming strategies such as walking away, wrapping in a blanket, conscious breathing, praise when you see them trying to put all of that into action, are all good.
So is refusing to engage with the topic at hand if the child is shouting at you - a form of stonewalling that seeks to address the problematic behaviour. For instance, if he is shouting that he wants X for breakfast and not Y, you address the shouting and ignore the breakfast topic until he is able to ask politely for what he wants.
The child needs above all to know that the adult is in charge and able to exercise self control.
There's plenty of evidence that shows that punishment etc doesn't work for some kids. For some it absolutely does work, but when it doesn't there's usually a root cause.
I did not mention punishment.