Ok, you all know AnnabethChase wrote an article about following Rick Riordan on Twitter. Here's the outcome of those clues:

Nico was in the Lotus Hotel so Zeus wouldn't destroy Bianca and NIco. Nico's mother was Marie di Angelo.

Percy "spends" his sand dollar by giving a half each to Hudson and East, two rivers. The sand dollar was payment for sinking the Titan's army on their rivers.

The Last Olympian had 381 pages in it. 382 is you count the battle map of Manhattan.

Nico's plan was to discover things about Luke's childhood, and to have Percy bathe in the River Styx. Nico's plan did not kill...