Can anyone help?

This is very difficult to answer because it will depend on what is causing his distress in the first place.  It may be useful to take a step back from trying to manage the outcome and try to identify some of the causes.  For example, does he have any sensory issues that are overwhelming him?  Does he have communication difficulties that mean he is struggling to express himself or feeling like he doesn't understand what is going to be happening in his day?  Are any of his routines being disrupted?  (Not an exhaustive list).  If you can identify any patterns to when these outbursts happen you may be able to mitigate some of the factors involved e.g. by reducing noise in the environment, using written or pictorial forms of communication (there are loads of ideas for these available online), recognising which routines are important to him and supporting him to complete them etc.

In terms of dealing with the actual outbursts themselves, what is likely to work again depends on the individual.  Some people respond best to some form of distraction, others to being comforted, others to some forms of clear boundary setting, others to just some quiet time and space to calm themselves down.  If he has a lot of pent up frustration that he can't seem to get out then I don't necessarily think that channelling that into something appropriate, e.g. hitting a pillow, is always a bad thing.  Without knowing your son it is difficult to make guesses about the best way forward (although prevention is always better than cure if possible).

When my daughter went through a phase of repetitive questioning what worked with her was limiting the number she was allowed to ask per day and gradually reducing it.  But her emotional arousal levels seemed to be somewhat lower than your son's when she was asking them, from what I have read here.

This is very difficult to answer because it will depend on what is causing his distress in the first place.  It may be useful to take a step back from trying to manage the outcome and try to identify some of the causes.  For example, does he have any sensory issues that are overwhelming him?  Does he have communication difficulties that mean he is struggling to express himself or feeling like he doesn't understand what is going to be happening in his day?  Are any of his routines being disrupted?  (Not an exhaustive list).  If you can identify any patterns to when these outbursts happen you may be able to mitigate some of the factors involved e.g. by reducing noise in the environment, using written or pictorial forms of communication (there are loads of ideas for these available online), recognising which routines are important to him and supporting him to complete them etc.

In terms of dealing with the actual outbursts themselves, what is likely to work again depends on the individual.  Some people respond best to some form of distraction, others to being comforted, others to some forms of clear boundary setting, others to just some quiet time and space to calm themselves down.  If he has a lot of pent up frustration that he can't seem to get out then I don't necessarily think that channelling that into something appropriate, e.g. hitting a pillow, is always a bad thing.  Without knowing your son it is difficult to make guesses about the best way forward (although prevention is always better than cure if possible).

When my daughter went through a phase of repetitive questioning what worked with her was limiting the number she was allowed to ask per day and gradually reducing it.  But her emotional arousal levels seemed to be somewhat lower than your son's when she was asking them, from what I have read here.