FFMPEG is needed only to convert uploaded videos and to extract thumbnails and other stuff.
It's not really needed if you grab videos from other tubes.
You can check my script:
www.automagick.com
With the new version, you can run a site like you want (by grabbing videos from several sources, like youporn, pornotube, empflix, tnaflix, and others) and if you like, you can make it grow in the future with your own videos, just like any other site.
It's a good solution to start, and also a good solution for a long term project.
Let me know if you have any questions.