1. In my opinion, should we create one database and each app access part of it using a key like tenant ID.
2. You will need to re-load the data with the changes and you can not change part of the diagrams.
3. Unfortunately, I was not working directly with a SOLR, it is better to wait for the expert answer. In any case it is necessary to compare the cost of data exchange between SOLR and Qlik Sense through the discharge in the file and a direct connection to one.
When a single database, you can always obtain data samples on individual elements and see the whole picture. If you have multiple databases you will need them again combine to produce a consolidated analysis.
The only obstacle to a single database option only be too complex data structure in the binding table.
If I understand correctly you are trying to build a mash up project using Qliksense by integrating charts into a web application.
I have a similar experience with Qlikview mashups where we used to have multiple customers with different customizations and data, what we have done is we use MYSQL as database and we had multiple databases for each customer.
As per your doubt you can even have a single database instance for all of them by have a ID to seperate the rows but if the structure keeps changing when a new customer comes it would be challenging.
We had a some experiences where customers used to come with different tables , columns and these customizations
are only for that , so we thought of having different databases for individual customers.
Hope it helps you.