I stopped working on proof of concept areas since I've discovered I can make decent looking desert areas with the toolset. I've done some work on implementing some of the quest ideas from the Anauroch sourcebook as sidequests. These are relatively straightforward quests along the lines of "merchant hires you to find something" and will make up some of the sidequests. Any obstacles for the player will go in later, puzzles, enemies etc. I've put in placeholder blank areas so I can put in the area transitions.
I've worked out a basic outline for a main quest and put in placeholders to support it. These are generic named npcs such as "shaman" and their conversation say things like "go click the clicky first!". While the written down plot outline has more detail than that, some specifics will be worked out over time as they grow into their spots organically. I haven't worked out the details of the ending yet, but that can come later as I currently don't have any inspiration for it. I'm not going to work on something like the endgame when I'm not feeling inspired, the lack of inspiration would show.
One big thing to come later, specific dialog lines for npcs. I try to find "voices" for the npcs so not everyone's dialog reads the same. Placeholder conversations will allow me to do basic testing of the main plot. The basic testing will focus on ensuring the story flow of the written outline is translated to game dialog correctly, making quest options show at the right times for example. Specific "voices" for npcs can come later.
Next step is setting up a test module and putting in these npcs/script to allow me to run through things and do basic testing of conversations and scripts.