Both 1 and 2 work the same with runtimes as they do with a regular FileMaker file.
Seems like the main question is how to have split data - interface files.
In your interface files, each table occurrence (these are the "boxes" in Manage | Database | Relationships), would use an external data source reference to refer to a data source table in the data file. When you double-click an existing table occurrence or create a brand new table occurrence, you get a dialog where Add Filemaker Data source is one of the options in a drop down and this is how you can select a table from a different file.
Once you have set up your table occurrences to link to tables in the data file, you can access them from your interface file exactly as though the tables were physically present in the interface file.
Clicking a button in a portal to see a detail view of that portal can be as simple as a one line script step that uses Go To Related Record to switch to a different layout and display the record you clicked.