Would need a little more on the data model here but I’ll make some assumptions.
- Account is a Data Reference.
- Data references have patterns to show more details or links to see more details
Event driven UI approach with action sets in Traditional was the right approach but in Constellation you want to show mode details about that Data Reference (even if those details come from an external SOR).
Examples
Based on selection of a data reference you can show additional views
Image from 
Webinar Replay: Achieving outcomes in Constellation: Solution Designing and Building for Success last week.
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Another version of this I’ve been working on this week
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Another i created for a forums post last month (I think this was for another of your questions)
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And a video with this working
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Additional View
These require a little more configuration and visibility conditions that force server refreshes (when rule conditions not the “always” condition).Can share a video on this if needed.
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Mixed data model
Where I am unsure on approach, from your image here.
This is clearly embedded data, as you are trying to capture details form the user (and help them by prefilling those details). I am unsure if there is a way to mix the UX as you have - data references and embedded data are separate views.
You can show data reference details inline, and choose what to display.
However, a read only data reference is always a hyperlink to the object itself
Additional approaches
I’d be curious on other’s approaches here.
I can think of a few other ways to do this but haven’t tested them to see how usable they would be in your specific scenario:
- Field Groups to have a more logical grouping of data
- Use the data reference preview above so users can see more details about the account as needed
- Use a dynamic text rule in Additional Information, Helper Text, Instructions etc. to show the required information to help guide the user input the correct information in the fields. A few screenshots as samples:
- See Clearer Forms, Happier Users: Out-of-the-Box Ways to Add Context in Constellation for a full outline off all the different ways you could do it
