I'm glad you are trying out the game and I hope you enjoy it. I'll try to answer your questions:
(Q) The rules say a player may trade in an unused Clue Token for 1D6 cards from the discard pile. Yet does the player have choice in how those discarded cards are drawn?
One way the game can come to an end is if the Action Deck runs out of cards. This was intended to give the players an extra turn or two to wrap things up. It was intended that the cards come right off the top of the discards... so, there may be some benefit to doing this at the right time.
(Q) If a player runs out of cards and dies as the result of an Attack, the rules say he is to return to the Village, select a new pawn and draw two new Action cards. Does that occur immediately, or does the player wait for Step 1 of the NEXT turn to get his two Action cards. (Or, said another way, in Step 2 of the next turn will the player hold 2 cards or 4?)
The player will select a new pawn and draw up immediately. They will have 4 cards on their next turn.
(Q) If a player uses a Clue Token to divert an attack, can the attack be diverted to a Villager instead of to the player (just as with the "I'm Over Here" Action card)? (Presmably if it's diverted to a Villager the Villager dies.)
No... that's just mean, why would you do that to the poor villager.
(Q) The Unwilling Sacrifice goal refers to a "victim". Yet who is this victim?
The victim is one of the villagers that you drag to the top of the waterfall. If they are unescorted they will run back to the village pool by the next players turn (quick like a rabbit).
(Q) In the Call For Help goal, does it require an Action to fix the radio?
Yes, that is a typo. It should be one action to fix the radio.
(Q) What happens if the Willing Sacrifice goal is drawn at a time when only 1 token remains in the game? Does the player owning that token lose? Is another goal chosen?
Then you can go out in true horror movie fashion and do the right thing and die to bring peace to the evil of the island. I guess you could call that one a win if you are able to finish out the cinematic ending.
Hope this helps, and I hope you will give some feedback when you are done playing the game.