Update;
Solved this, with the help from godot discoord :).
In my world file, i dont need to instance the level, just add it in.
Level mainHall = new Level("res://maps/map1.tmx", "mainHall");
AddChild(mainHall);
However, since the Level class contains the packedScene for the Tiled level, that needs to be added as a child for that to show;
public Level(string path, string name)
{
Scene = ResourceLoader.Load<PackedScene>(path);
Map = Scene.Instance() as Node2D; // Getter/Setter
this.Name = name;
AddChild(Map);
}