The first 3 questions have all been answered basicly by the same answer. Impression in ground, possibly a block n tackle hanging in tree. Once digging they found the platforms and the rest is history.
4th question. Well no one did, but we know someone had a plan to come to area to bury it in a deep pit.
The block & tackle is a later embellishment to the story. The story is variously told as a depression in the ground next to an oak tree
- with a limb over the depression including a block & tackle
- with a limb over the depression having marks as if it once had a block & tackle
- with a limb that had been cut off, as if to hide evidence of a block & tackle
Honestly, we're not even sure there was an oak tree there.
Likewise, the platforms "every 10 feet" is also an embellishment. It is also told as "they found a layer of logs
at 10 feet" and that probably morphed into
every 10 feet. Most likely, the kids (or teens or young men, take your pick) would not have dug beyond 10-20 feet as that is a
very deep hole and no reasonable treasure would be deeper than that. Reality is, if these 3 guys saw a depression and dug a hole, there is zero evidence anything was found. If they had found treasure, it's unlikely it would be the only part of the story that didn't get out.
Finally, there is no reliable evidence anyone had a plan to bury anything there. The Duc d'Anville log has no reliable provenance. It just showed up one day. I'll leave that for another thread.