How to remove the ability for users to set up their own dashboard?

This has to be done by App Manager.

If you want to make sure everyone sees the same dashboard, you can set up the Dashboard control to "App Manager".

1. Click on your avatar at the upper right hand corner, go to "Manage Application".
2. Go to the "Governance" tab.
3. Select "App Manager' in the "Home Dashboard control:" field.

4. Go to the "Dashboard" tab. Select the tiles and set the limit in the "Home Dashboard Tiles" section.

To rearrange the tile, go to the Home dashboard page, then drag and drop the tiles to rearrange them.