Preview - the Arcane Angler's Fishing Derby event!

[Cinco]

...only one person wins the house items?

Top 10 all get the golden fish trophy for this year (I expect it will be a recurrent reward).
The Number One Angler gets the Title and the singing fish plaque trophy. Just one (unless there is a tie for first place).

The lootable crates need any type of currency to open?

The Pirate King Crate is locked and opens for 5 Platinum. The other is unlocked.

Do the bonuses from the elixers stack with any other source of buff?

The Fish Oil Elixir buffs are stacking!