Good afternoon @Dave65452 and @Manuel205009.
Definitely willing and able to sort some more tutorials on this topic. The Waveshare 4G HAT really is the leatherman tool for getting all mobile connectivity onto a Raspberry Pi 4 Model B and there was just much to much to pull out for a single guide.
Tutorials do take time to get them the polish I need them to be at. To save you waiting here are three guides (from external websites) that should help in your situations.
Creating a Hotspot/Constant Internet connection with the 4G HAT that can then connect to your Raspberry Pi can be done this way -Super SIM, Raspberry Pi 4, and the Waveshare 4G Hat Getting Started Guide | Twilio
OpenWRT OS is also an option for getting internet connectivity and turning your Raspberry Pi into a full-on router - [OpenWrt Wiki] Raspberry Pi
Finally, I stumbled across another guide as I was writing the Python Scripts for the system. The hardware is a little bit older than what I used here and I couldn’t quite nail it in before shoot day. The end result is a 4G Raspberry Pi System that you can text Terminal Commands directly to it. They run as they should and the output of the Terminal is then texted back to you. I reckon that’s exactly the interactivity that you’re looking for Dave. - Remote Control of Raspberry Pi Via SMS (RPi SMS Shell)
Hopefully, this keeps you pushing forwards, expanding your edge, instead of waiting on me 
.
Kindest regards,
Tim
