This is great OP! The earlier it's picked up the better as everything moves sooo slowly. It sounds like neurodiversity is in your family and that can include ADHD, ASD, dyslexia, dyspraxia, dyscalculia - he might well have a combination.
DS has ASD and dyspraxia, always had good speech, met all milestones, a little clumsy but early crawler. The dyspraxia became more obvious as he got older when using a knife and fork/riding a bike/tying shoelaces/hand writing (although he can do all of them even if it looks a bit awkward). I would say that it might be worth getting his hearing checked - glue ear is common in those with ASD and may be making him louder.
With how to treat him when he doesn't have a diagnosis, don't worry about it, you can parent him as if he has ASD/ADHD/dyspraxia without knowing if he does or not and it won't have a negative affect if he doesn't. Basically, very calm, very clear, very patient and very consistent.
So lots of warning before any transition if he struggles with transitions, 10 minute, 5 minute and 2 minute for example, ND kids often need time mentally to feel like they've finished one thing before they are ready to move on to the next.
Make everything into a fun game - who can get their shoes on first, can you get your shoes on before I count to 10, can you do a magic trick and get your shoes on while I get my coat on - that sort of thing. Make it sound really fun, amazed face and lots of praise at how magic he is or whatever if he does it.
Routine - try to have a clear structure to what happens through the day, especially at weekends, make sure you build in time to burn off energy if he needs that and also time to decompress.
Avoid places for now if he can't cope with them because he becomes quickly overwhelmed - soft play, birthday parties, group meet ups, public swimming pool - or just stay for a short time and leave before he starts becoming dysregulated. You will find you need to be aware of what he is doing and watch him more carefully than other parents so he doesn't get to the point where he is overwhelmed and starts lashing out.
Low demand, him constantly saying 'no' could be PDA or it could just be the terrible twos! Try not to be constantly asking him to do things, stick to only asking if something really needs doing. Do lots of things 'together' to take the pressure off and make them fun if you can.
DS is now doing a degree and working as a software engineer, very happy! Good luck OP, you got this!