1°)You can preview,using the incompleted file ".bc!" in the download folder. I recommend VLC player
But you can only preview what you have downloaded, and the files download in tiny parts randomly, so if you have 50%, chances are you can't see more than the 5 sec. of the beginning.
2°)The seeders are the number of people who already have downloaded all the torrent files and are uploading them .
The leechers are the number of people who are downloading and also uploading at the same time.
The peers are the seeders and the leechers.
Among all those, not everyone has the same internet speed,not everyone is connected to everyone, and not everyone shares or downloads only one file.
So yes it is quite possible, but the more you upload, the faster you download.