I can share a bit about our experience. We've known our daughter had ADHD since she was a toddler. So obvious. Didn't bother to get her diagnosed until first grade, when we needed the IEP to fight off an insensitive teacher. She's in seventh grade now and doing great.
We don't (yet) have a behavioral therapist, but I can recommend a psychiatric practitioner if you decide to go that route. We agonized over it for years. One thing that helped was to browse the ADHD subreddit - reddit.com/r/ADHD. It was enlightening to read about kids struggling with ADHD and their experiences with medication.
It's hard to get appointments. Doctors are overburdened, especially with covid. Luckily some pediatricians have started added this to their practice. For example, Ballard Pediatrics added someone to their staff recently.
I can share more if you want. It's scary when you get the diagnosis. You aren't alone, don't worry.
I don't have a therapist to recommend, but cranial sacral therapy has been working well for our family. We love Elizabeth at soundsomatics.com. Also, cutting down on dairy, eating less processed foods and ensuring movement each day is a must at our house.