Your internal networking should not be affected when you use ULA - those won't change, and IPv6 devices tend to have multiple IPv6. Yes, it won't allow you to a

Your internal networking should not be affected when you use ULA - those won't change, and IPv6 devices tend to have multiple IPv6. Yes, it won't allow you to address your internal nodes from the external network, but that is something that you didn't have with IPv4+NAT either.