Hello!
I would like to help you with OpenVPN configuration.
If RPI loses internet connection when OpenVPN client connected - it means OpenVPN changed default route, so it's just OpenVPN server setting, I can solve it of course.
About my experience: I have big experience with OpenVPN servers\clients. OpenVPN on RPI. Experience with variety of different configurations OpenVPN servers, such as serial connection 2 or 3 OpenVPN servers, for maximum security. OpenVPN over IPv6 protocol. I have big experience with network administration and pfSense. Experience with VMWare ESXi, MS Hyper-V, Proxmox VE, Mikrotik, Ubiquiti and some different skills.
My another skills and reviews you can see in my profile.
Hope for cooperation!
Thank you!