I'd announce now! You'll have a lot of support and people happy for you. And in the worst case scenario if something were to happen you would have that much more support to get through it! Good luck and.congrats!!!
Things are much safer after the first ultrasound, so maybe after that... I will say, we waited to tell people after the first trimester was up, but miscarried at 10wks and I had to tell everyone "well I was pregnant..." in order to get the comfort and support I needed. For me, much much harder. I am pregnant now (39wks) and told close family and friends after an earlier ultrasound. It is a tricky route but congratulations, I'm sure things will go perfect for u!! :)
I also have PCOS! Ugh! I don't have as hard of a time getting pregnant as you tho. I told my mom and dad right away at 4wks. My husband told his father when I was around 12wks. And we told everyone else at 18wks. I had a miscarriage previously and didn't want to tell people and have to explain later why I wasn't pregnant so we waited a long time. But a lot of people tell sooner. As for your kids id probably tell around 12 or after your check ups to see if everything is going well.
CONGRATS! I couldn't imagine waiting so long to have a baby. I'm sure your family will be so excited:) good luck to you