Helmets are a whole other rabbit hole.
Personally, I'd recommend a cheap PASGT for now just to get your head protected, then you can go around looking at whether you'd like a MICH style, something Russian flavoured, or one of these high-speed climbing helmets the kids like these days.
AFAIK you need to start with a good enough helmet to be able to securely mount anything to it, and balance the weight properly, and all kind of other stuff. You can easily spend $300 on a helmet that won't break your toys or your neck alone.
A cheap PASGT might not be trendy, but it will be ~$30, fits a watermelon, and you can throw that gopro on your other shoulder or your gun.
I could learn from someone telling me I'm wrong, though.