After gathering knowledge, I decided to use the Modelling mode PolyGroups editing tool to first blockout and then create the level. A very helpful idea was using the layout designed when concepting as the reference plane of the Maze walls location and players journey.
Constructing the level was a tiresome process, first creating boxes as Dynamic Meshes (as files tied to the level only, not the whole project), resizing them, then inserting loops into and extruding into the shape of the walls. Bigger chunks of geometry created that way were merged and saved as Static Mesh into the content browser. After that they could be edited and textured in other software or further manipulated in Unreal Engine.
A workflow of this sort proved to be a dead end - too ineffective to create the level of size I planned to. Adding detail to the Maze created that way would also be a time-consuming process.
Character size guides
Reference plane
Creating geometry in Modelling Mode as Dynamic Meshes
Editing geometry with PolyGroups tool. Inserting loops and extruding.
Part of the level merged as the static mesh