I want to thank you all so much for your responses.
I am by no means self diagnosing, just recognizing signs/symptoms/traits. So far everything I have read about ADHD seems to describe things I have noticed in my boy, so I'm trying to learn what I can to help balance those traits - be they part of ADHD or just part of the unique individual that my child is.
He may have ADHD - obviously the things I have described about him above are just an incredibly tiny part of the picture, there are many other things I've noticed that are pointing me in that direction - or he may just be 'him' with all his strengths and challenges. To be honest at this point the persuit of a diganosis isn't my priority - it may become so later on. My priority for now is to follow my intuition which is telling me to read and learn. It's telling me that this may be relevant to my child, so I'm going to find out all I can in case it is.
So far I've already made some changes, reflecting on times that he is more focused or less. Things like making sure he has regular snacks that will balance his blood sugar, making plans for the next few days with DH (he's off work) for us to take rainforest walks so he's exercising and among nature more, replacing cartoons he watches with documentaries as the former tends to make him more hyperactive or distracted and the latter more focused. Lots of others but you get the idea. I've also had some very helpful PM's which have given me insight and ideas.
I'm taking him to the Dr next month for his four year old checkup and I may have a chat to the GP about it then.