The strengths and weaknesses of different VPN protocols April 26, 2019 https://securityaffairs.co/wordpress/84506/digital-id/strengths-weaknesses-vpn-protocols.html
Many commercial VPN services support them all. But for users, it's one or the others. There's no combination.
Too new, I guess. See https://www.stationx.net/wireguard-should-this-be-your-new-go-to-vpn/ AzireVPN, IVPN and Mullvad offer it. And maybe others.
i think wg is no more or no less secure than the industry standard ovpn protocol (for the time being). it should be implemented by vpn service providers for those who want to use it. https://courses.csail.mit.edu/6.857/2018/project/He-Xu-Xu-WireGuard.pdf
Yes, I guess it is to new and not widely used yet. I know that Mullvad has this option, I will just wait until Windows is supported and will give it a try. I agree that it's probably not more secure than other solutions (small attack surface and simple code is debatably it's biggest security advantage) . I'm more interested in how easy it is to set it up and how it is performing. At least that is something they say is improved with this protocol: https://www.wireguard.com/