If you're filming someone talking to the GoPro, try and point it at their chin, that way their whole head will be in shot, not just the top of it.
You can change the lens screen on the new Hero 5. I didn't realise this and it put me off buying one for a while because once the screen is scratched you're stuffed.
The built in stabilisation on the Hero 5 is actually not bad.
I never shoot my films in 4k. Most people will be watching them on their mobile phones so what's the point? The data would kill my MacBook anyway.
I shoot in 2.7k which allows me to add more image stabilisation in post production and output at 1080p.
Shooting 50p helps smooth out your footage out, especially if you don't need it to play back in normal speed.
My GoPro is hardly ever my main camera.
A lot of people shoot on GoPro. A lot of peoples films look the same.
I spent a little bit of time learning the basics from Google and YouTube then just went out and started using my GoPro. In the end I built a workflow that works for me. It might not work for you. 70% of what you need to know you can learn pretty quick, the other 30% probably doesn't matter. Probably.