Hardware upgrade REALLY needed?

There are many layers between your modem's channels and the TCP/IP applications you've described, and your post doesn't take into account your actual devices, their OS and apps, your router, or security considerations.

Gigabit Internet is a marketing term based on your signaling rate. It's not predictive of the speeds you'll achieve across the Internet.

You may have competition for bandwidth at any given hop. You don't trust Support, and claim that Panoramic WiFi is unnecessary, but I personally recommend it, because it will ease your management issues and you won't need to pore over numbers in a status report that tell very little of the whole scenario.

But you're using the consumer home connection for multiple users in a commercial activity. Have you considered a Cox Business account with a properly specified contract and service level?