I feel for you. My ds is four and a half, and I've struggled with his behaviour for a long time. I've posted on here before, and with the help and advice offered, stopped trying to look for an 'answer'. My ds is so destructive - his tantrums are legendary, and in trying to 'pick our battles' and 'ignore' behaviour we have founds ourselves treading a thin line between being on eggshells all the time, and being to lax with his aggression towards his siblings. I don't just look for the negative (he is sensitive, kind, full of energy, lots of fun - I love him, he's my son!!) but he drives me crackers with his rudeness towards me, for example spitting in my face, screaming at me etc. I won't tolerate it, but if I then put him on time out, I know we've got to go through nearly an hour of screaming and bellowing, and he has starting peeling the wallpaper off at the bottom of the stairs. Even just saying 'no' can result in a meltdown. For example this morning "Can I feed the baby?" - "No ds, I'm feeding the baby, I always feed the baby. Could you pass me x for the baby?" resulted in "No NO NO!!!" then "I'm going to tip this water over" etc etc, until you feel like you've been through the mill and back.
I'm wavering over contacting my HV again, as I'm worried that this behaviour will get worse when he goes to school rather than better, as he will be even more tired. I've noticed it is worse if he is tired and/or hungry, but there are times when he's basically hungry because of his behaviour, i.e. what should take a couple of minutes has taken forever.
I have three girls, and find their tantrums/wilful behaviour etc challenging, but not a patch on my ds. I'll be lost without him when he starts school but I really feel for you struggling with it, as it is not easy and there are no easy answers. I've read so much, watched so much, listened to so much, but still can't really work out what to do.