You can load torrents in rtorrent from the command line.
wget terminates after a download. You can add the exit command to the on_finished event in your .rtorrent.rc.
If you need to run the application in the background, you can use the screen management utility, or the & operator.
If you want to watch the file download, you would simply omit the screen management.
Another solution is to get rtorrent to watch a directory for torrents. When a download is complete, you can specify which directory it will get moved to. To start a download, you move your file into the watch directory with your script, and check for its completion status by checking the "completed" directory for files.