most (not all, some contributions are QTVR-only due to historical reasons)
many, but depends on photographer's choice of file upload (newer event = more likely to work) and your device's capabilities. You may experience slow playback, distorted images or unexpected browser quitting if there is only limited memory/GPU power available.
I used 8 bit source images. Each of the 5 source images were produced from 3 images (underexposed, normal and overexposed) by enfuse. This was to produce much better looking images, thanks to Erik Krause :)
Equi-rectangular image was converted to QT with registered version 1.6.2 of Pano2QTVR pro.