Hi sorry was out and busy all day, but I am home now and settled in front of my computer :D
to answer your questions:
1) there are lots of generic and fragment digsite spawners around each lot and up and down the beaches. so I play with needing all five pieces each time... but for an easier play the first time you can try it with buydebug after finding the first five ... but honestly I don't think you will need to :)
2) The challenge lots are numbered in the world, but you can choose any lot you want after challenge 4.
3) yes any collectible will count, any item you can click and: fish, pick, harvest, or collect in the world will count as resource material. yes to all and 5 collectible=1 square ... you can use less, but I think you will then find it too easy ... but if you find it too difficult change it up and use 3 or 4 per square ... adjust it to fit your playing style :) I personally use 5 and find it challenging but not too hard!
I would love to see screenies of your sim surviving :D
