Wow, Chris! That's a really helpful answer. I apologize for being so slow to reply.
I am very interested in your castle. My table is smallish, just 3'x4.' A castle with an attractive keep and some walls is pretty much what I need. A very approximate size could be anywhere from 8" to 12' square, which would allow for a small siege scenario, or to just be a place marker/scenery for a battle taking place near a castle.
In the case of a siege, being able to fit half a dozen 40mm x 80mm stands in the courtyard would be sufficient for my own needs.
The doorways don't really need to match the same scale as the figures themselves, as long as it's not wildly out of proportion. On a small table, I have no issue with using 10mm buildings with 15mm castings.
Of course, not all castles looked like Matsumoto or Himeji, so a modest frontier fortification is perfect.
Thank you, Chris, for asking what I'd prefer to see. I'll happily follow your progress, and will be excited to purchase what I can.