Shelley,
Firstly an answer to the easy question: the flowers are falling off, starting from the bottom and working up, because the the plant is coming to the end of its bloom cycle on that inflorescence. PERFECTLY NORMAL
The second problem is a bit more confusing,
but it appears to me that you may have gotten mold spores into the top of the mix to form the "moldy look" on the roots and top of the media. Temperatures in the range you gave as well as a somewhat humid environment will cause these spores to proliferate. From the photo, it does not appear to be mealy bug, the other alternative for "white stuff" on plants.
I think the easiest solution is to repot the plant into a larger pot and into fresh mix of your choice depending on where you live and your conditions. Cut the root ball to no more than about 3-4' long from base of pseudobulb, remove as much of the old media as possible with a pointed skewer, wash with a hose thoroughly but carefully and allow to dry on a newspaper for 24 hours before potting up. I like to allow about 2" of growing space around the plant when I choose my new container.
CL