I am doing it again this year.
As there were no practical limits, I went to town with the orchestra last year: double woodwind plus cor anglais and double bassoon, full brass (very high horn parts), lots of percussion, two harps, organ and strings. It is all very impractical, but essentially it could be played. Other pieces last year were not playable, so I think this year I will stick to actual (synthetic) instruments, without consideration for the practicalities of human players. It will also be much Scarier.
I have a new temporary blog for Scary 2015; I am The Guiser.