Regarding GALV Layers, please remember that, right now, only static layers bound to the player or an event are supported. I will add more functionalities in the future.
Viewing post in Minimap for RPG Maker MV & MZ comments
GALV Layers lets you choose a "character" to bind a layer, that is either the player or an event. When you leave it empty the layer sticks with the map.
Right now, the minimap supports only static layers that are bound to the player or an event, so I suggest making an invisible event where your layer should be. I'm already planning to support static layers that are not bound to a character, too, so you can also wait a few days until I release the next update.