As long as you plan to try Dungeon Crawl Jam (I might not remember the name correctly 
) it would usually suggest procedural (random) map generation, as it’s one of the not always obligatory but still important features of the genre. This way your map would be generated by code and filled with assets made in Blender or other convenient 3D editor.
If you’re planning to make a “static map” which doesn’t change or only parts of which change - it can also be made in Blender, however, there are several bottlenecks to be aware of (and I’m not aware of those as I’ve usually been doing procedural generation 
) especially in case the map would become large and will contain a lot of assets.
I don’t think there is a quick way to import Quake 3 map currently. On the other hand GLTF format is read perfectly.