Hello!
I did something similiar (adding new message), however I was using MAVProxy for debug.
Try to read something here, maybe it will help:
https://discuss.ardupilot.org/t/new-message-and-variables-in-apm-planner-2/11641/19
If you have any questions feel free to ask.
MAVProxy is easy to edit (when you add new messages for example to mission planner, you have to build it over and it takes long time). In mavproxy terminal, type ‘status’ to see all incoming messages.
What I see from your code, you are trying to find appropriate port of instance 1, why are you using instance 1? Did you set telem2 in any GCS to MAVLink protocol?