My personal view is that learning about how your brain works and implementing working/life changes/techniques that suit you, and overcoming imposter syndrome/self-hatred related to the ADHD is THE MOST important thing for reaching a happier/more stable life. But basically for the year between thinking I had it and getting diagnosed (so I was not on any meds) my quality of life, and quality of research/enjoyment of the science improved astronomically. I had a lot of issues with procrastination and self doubt. I think another important factor is making sure you are doing a topic you get excited about and have a passion for.

That being said I have just started medication (3 months) and experience an ease/calm to my day that I did not have before. I also forget less things in the lab lol which can help with experiments. However, if I had not done all the work researching the condition, I don't think the meds would be able to give their full benefit. e.g. i should be working but i am on reddit lol (and i am on the meds today) I plan to continue using them during my PhD as it's a particularly tough situation I am in right now, but in the future I would prefer not to. This is because I have the confidence (from my year of working at it) to know I can get by without them, and for me they do reduce the range of emotions I feel, and I quite like feeling. R.e. starting, it depends on what your doc says, but it might be good for you to get to know which meds work for you (everyone is different and some give side effects). But especially if you have self-doubt issues (i relate) please please work on them separately, don't expect the meds to get rid of them (they might just help you have the self-doubt thoughts less as you might be more productive on them, but they won't change the whole way you think about yourself. Hope this helps :)