Are there best practices or maximums on how many records can be hosted in a single app?
From an engineering standpoint, we optimize and test features around the 500,000 records limit. That being said, our largest apps that are used in production are around 200,000 - 300,000 records, so you might run into some issues with 500,000 (especially if you have a large number of fields e.g., 100). If you have any trouble with calculation fields, exporting or workflow automations for large apps, let me know!
Cheers, Ben