On the main page you should be able to display at least 12 favorites instead of the 4 before it tells you to show list. So there should be able to have an additional two rows visible.
It’s by design if you have background image enabled.
It would be nice to let the user chose. 4 is arbitrary.
It is limited to a single row, not necessarily arbitrary (some devices / orientations it is 6, since that fits into a single row).
We have more plans for the new tab / home page in the future, and having so many combinations makes supporting new features more difficult. Limiting to one row allows us more flexibility. Hopefully things are more clear in the coming weeks / months.