Okay so I'm planning on crafting the Celestial Observatory but it occurred to me that I have the maximum # of houses. (I would buy a house every time I reached max gold and filled my backpack and bank) Would I be allowed to craft the observatory if I've maxed the houses I can have?
Unless you sell a current house, you will need to purchase an Additional Castle Elixir before you can craft your Observatory.
If you have the maximum number of houses when you attempt to craft the Celestial Observatory, you will notice your crafting button is greyed out, and placing your mouse over the button will pop up the wording that you have the maximum number of houses, and cannot craft this house.