I have a GoPro Hero 4, Black Edition, bought in 2017.
So, when I got my ST1100, two years ago, I wanted to use it whit my GoPro.
Before gluing any kind of support on my then brand new helmet, I wanted to experiment first.
So I got an action camera helmet chin strap support, from Amazon, for about 20 Canadian dollars.

It is not glued, it is just two thin nylon straps (1 cm or half inch wide). So, I can still close my visor, and it doesn't affect my field of vision.
Me too I tought of mounting it on the bike, but I realised that one big advantage of having it on your helmet, is that you can just turn your head and look in the direction of what you want to capture.
A second advantage of having it on your helmet, is that when you park on the street... you can't forget to remove your camera. It stays with the helmet, or I can detach it in 30 seconds.
Another possible advantage : less vibration than directly fixed on a bike part.
And on the chin of the helmet, it is also protected against wind by the windshield.
But, to be honest, I have to admit that (have to choose my words here) from what I saw, those who extract single frames from their videos, while riding at 170 kmh, have lots of blurr in them.
A cool feature of the GoPro is that it can show you your actual speed, thanks to its internal gps.
But... who drives this fast at our ages ?
As for sound now... GoPro camera are a bit tricky. They have a small hole with a microphone inside the device, like cellphones.
But those microphones are very very sensibles. Any simple breeze will make a blowing sound, like most camera when you are recording outside when it is windy.
I bought an outside microphone, like one that you can use with any cellphone or tablet, but discovered that you can't use them with a GoPro.
You need to buy their GoPro microphone adapter (probably adapts the impedance) that they sell for about $100. A real Racket.
I thought, maybe I could use a small audio recorder. And then later add that to the video. But... what do I need to record exactly ? Not sure I really need this feature.
One last thing I want to test one day, is to simply put a piece of temporary tape on the microphone hole.
This will cut all the high frequency noises, but the low rumble frequencies will still go thru. A bit like when are wearing earbuds.
If I ever post one of my riding video on youtube, the only sound will probably be some music with it. And very little text to describe or explain something if needed.
One last thing... I will soon experiment another mode I didn't use much, and that might give better result than video.
I have a mode where I can set the GoPro to take single pictures, every number of second I want : every second, every 3, 5, 10 seconds, etc.
I once noticed that those images are of greather resolution than single frames extracted from video. I guess one picture every seconds might be OK for my need (mainly for capturing beautifull landscape and routes).
I bought some spare batteries and memory cards.
I also have a small rechargeable pack that I can plug in the GoPro and use as an external battery.
And... Oh Yeah. To turn the Camera On or Off, my GoPro is connected to my phone's bluetooth.
So I stop at a secure place, take my phone, start the GoPro using the App, and Voila.
I can also press the little button if I remove my gloves.