ADHD diagnosis as an adult - where do I even start?

I have the doubt of whether I'm ADHD since after I have given birth. It started with me suspecting that I had post partum depression and had reached out and talked to professionals to get that under control. And then in a few occasions my husband made some remarks that he felt that I might have ADHD.

Looking back as a child I always had problem focusing but I could also be hyper attentive to things that I enjoyed, especially things that I was good at and found a sense of achievement. My procrastination has been quite bad even into adulthood. I found a system to work on and have appointments religiously marked on calendar and set plenty of reminders. But even important things I could have forgotten. Not that I am not capable doing them but sometimes I just don't want to, or sometimes I just forget.

I don't have a lot of friends. But for those that stick around we are close. I'm always told that I'm a bit weird since I was a kid. Got bullied a bit in primary school. I'm a perfectionist on things that I excel. I hate tidying up, but when I have the energy and motivation I can spend hours reorganizing the room and can't stop until I'm done. I'm sensitive to what people say to or think about me. I can be restless but there are days that my energy is so low that I don't want to do anything at all. But on days that I'm full of energy I can be 200% productive.

My brain is always spinning and can hardly stop. I have taken extra effort to over compensate things that I'm not good at and I think I get to a point that I'm quite good at masking. Luckily because of my interest I did quite good academically and am doing reasonably ok at work. Though sometimes the extra effort that I put in behind the scenes can be exhausting.

When I look at my kids I'm worried that one of them can be on the spectrum or may have ADHD. As a person growing up without knowing what ADHD is and didn't have any support, I want to get proper diagnosis and be able to offer support to my kids if needed. Where do I even start? I checked online there are psychologists or psychiatrists. Do I have to first go to a GP to get a referral or can I go direct? There are also online only appointments. Is it better to do it face to face or is online ok? What's the process and it seems like it can get expensive? Any recommendations on the clinic in Sydney? Sorry if this has been asked before and thank you so much for your help here.