I believe the issue tracker url can be whatever you want/have for an issue tracker address.
The update JSON format I believe is this: https://mcforge.readthedocs.io/en/latest/gettingstarted/autoupdate/#update-json-format
They serve different purposes:
The MOD bus is for lifecycle events (registry events, etc) and the FORGE bus is for gameplay events.
They are separate because they are separate classifications of events.