Keep in mind that the Dynamics 365 (online) limitations still apply at the platform level. For example, if you are connecting to SharePoint, by default, all your apps will hook into the SharePoint structure. Also, any limits on the number of "resources" also apply at the platform level, for example, number of entities, access teams, workflows, and active business process flow per entity.

Another limitation is related to the underlying schema. Attributes will have the same display names across the different apps. You will be faced with challenges when the different user groups want different display names for attributes in common. Furthermore, not all entities support multiple forms. Appointments being one of them. Default views, search views, and associated views are in common as well.