My first baby steps will be:
A first set of prefabs for modular dungeon layout
Floor
Ceiling
Wall
Up stairwell
Down stairwell
[*]Dynamically build the dungeon with Lua based on a hard-coded layout
[*]Use stairs to move between levels
That's it for the first set of goals! Gotta keep it simple and doable. So far I've got floor, ceiling, and wall prefabs done and I'm starting to look into dynamically placing them with Lua. The textures and geometry are just whatever I could whip up easily and so they don't look great, but one thing at a time.