Yea actually you would better use an external hard disk .
But I guess you want to use FTP because you don't have a hard disk ..
Ok look I'll tell you something better which will save you time and money and is pretty easy to do.
1.Make a torrent on the 1st computer , and in that torrent include everything you want to transfer. Make the torrent private.
2.transfer in an email attachment or USB flash storage the torrent file to the other computer.
3.Now every time you turn on both computers the data will transfer.
I think using a torrent is the best, since you also can freely shutdown and reboot computers, while with FTP I guess you'll lose most progress if there is some blackout.