I've really enjoyed going through your PDF of Mystara, there is a lot to draw from there. I've already got many of Thorfins maps for 1000 AC, but your overview of the world is both concise, and broad enough to give a really good feel for the place. I'm going to use Keep on the Borderlands, The Lost City, and elements from Lost Mines of Phandelver to run an introductory campaign for kids. I think your PDF is the final piece of the puzzle I was looking for. My 8 year old daughter spent a day making a Hin Master cleric. Thank you.The thing was lost city is that it's a bottle model. It literally starts out with just a 20 x 20 room sticking out of the sand. You can put it anywhere because everything takes place Underground. In Canon it's in the nation of Ylaruam but as long as you've got a small stretch of sand you've got an adventure. The people don't resemble any of the surfaces because of their isolation, so much they have their own human variant.
Having run it I will say the bane of the module is the create food and water spell. They didn't have it in the original rules for the module and in fifth edition it ruins one of the major elements of the story