Thanks for the feedback!
Regarding 1: You're right. The current use case was always intended to link the selected issues from the issue picker field to the current issue. You are suggesting a reverse logic. That`s interesting!
I would like to know more about your use case. If you like, you can suggest a new feature at https://codecentric.atlassian.net/servicedesk/customer/portal/5/group/10/create/44. We are always actively looking for new possible use cases and ways to use our apps.
Regarding 2: You're right here as well. Our app is based on the Forge Framework by Atlassian. Unfortunately, this does not allow us to display our custom fields in some UI elements. We are also waiting impatiently for Atlassian to expand the Forge platform in this respect.