Why do I have to wait so long to start a large download?
BitTorrent allocates space for the file to be downloaded before actually starting the download. That means that BT writes a "dummy" file that has the exact size of the file being downloaded filled with zeroes.
Just give it time, after this is done, the file will begin to download.
BitTorrent is often slower at the beginning of a download than the end, this is due to the "swapping" nature of the protocol. Hang on there, the speeds will most often pick up