Hi Johan,
There are indeed quite some levels where settings can be entered. In the Model, in the Runtime configuration, in the IAM global configuration, in Web settings.ini, in Indicium inside the appsettings.json and web.config.
It depends which setting you want to set and how globally the setting should be applied. For instance, PageSize is normally something that could be applied globally (e.g. 50) and for some screens be deviated from as it can be set in the Software Factory at Subjects.
It's up to you where to apply these settings. For PageSize, I suggest putting it in IAM at Global configurations as there you have a good overview of the extended properties that are applied to your application(s). When developing the application and not using IAM, you can also apply it in the Runtime configuration in the Software Factory.
Did this give you enough information? We are happy to help.