We can generate the template for our tool starting from the mw.wbTemplates.store.values javascript object which contains the templates used to generate the wikidata pages.
We will probably need to extend the available templates with the ones we need for the Primary Sources tool.

A possible solution could be to add a mw.psTemplates object or even extending the wbTemplates object directly.
Another possible path could be adding our templates to the templates.php file in wikibase-view which declares the same templates.

I am still trying to understand which way is the best one as far as maintainability and best practices are concerned.

Another part in the UI is played by jQuery.wikibase, I still need to understand if and how this library is partially responsible for the templates generation or if it is just used to manipulate the DOM objects at later stages.

I'll try to add some more comments when I'll understand how to leverage both to obtain our final template.

@Kiailandi triaged this task as Unbreak Now! priority.

@Kiailandi: This task has been open for nearly two months. If this task has suddenly become a super urgent crucial task that needs to be fixed immediately, setting anything else aside (see the definition of the "Unbreak now!" priority), please elaborate why. If not, please decrease the task priority. Thanks!

In T168247#3506332, @Aklapper wrote:

@Kiailandi triaged this task as Unbreak Now! priority.

@Kiailandi: This task has been open for nearly two months. If this task has suddenly become a super urgent crucial task that needs to be fixed immediately, setting anything else aside (see the definition of the "Unbreak now!" priority), please elaborate why. If not, please decrease the task priority. Thanks!

My bad, fixed.

It has always been one of the top priorities as a task, but I suppose the best priority is high.

Will fix the other tasks in the same way