Hi Daniel,
Thanks for the feedback.
The key to understanding how to author a layout in ArcGIS Pro is understanding what a map frame is. A map frame is a container on the page layout that points to a map in your project. The map contains contains the layers, along with other properties that the map frame inherits.
You can have X number of map frame on Y number of layouts all pointing to the same map. Each map frame can have different extents (this includes time and range extents). You can X number of map frames on the same layout all pointing to the same map. However, all map frames are dependent on the map on what layers are available in the map. If you want different layers for different map frames you will need separate maps. See Add and modify map frames—Layouts | ArcGIS Desktop for more information.
Extent indicators - Extent indicators—Layouts | ArcGIS Desktop - can be applied to any map frame in the layout providing that there is another map frame in which to reference. It does not matter if both map frames point to the same map, or to different maps.
There is more detailed information regarding the steps to create a reference (overview) map in the section "Add an overview map and extent rectangle" within the online tutorial - Make a layout—ArcGIS Pro | ArcGIS Desktop.
As far as the poor rendering of the legend text could you provide an example screenshot?
Hope this help,
Tom