This sounds really fun. I never played Castaways but the idea is cute. I think there's an error in your math, though. If each square costs 5 resources, then a 3x3 lean-to would cost 45 resources, not 9. There are 9 squares @ 5 resources each = 45, yes?
Edit for questions:
1. After you find the 5 pieces to create the dive-well in the first challenge - in successive challenges you must build a dive well. Must you find the five pieces again? Or can you buydebug, and pay the 5 resources per square?
2. You reference Challenge lot 1, 2, etc. Are the lots labeled in the world you created? How do we know which lot is which? Obviously the first lot will have nothing on it, and I think you mentioned what was on the lots for challenges 2 and 3 - so for challenges 4 and 5 - will any empty lot do?
3. There was something else, but I don't remember what it was now. Oh wait... I remember. I'm assuming any collectible counts as a resource. So seeds, minor pets, wildflowers, etc. all count, yes? Do items found in a dumpster or at a junkyard count as collectibles? If they do, if the collectible takes up more than one square, do you get 5 "credits" per square of the collectible or does one collectible = 1 square no matter what?
I think that's it. For now. :)
