Its also getting the content creators onto the new platform. Thats a bigger challenge I think, without creators it's a dead site really, and making videos is significantly more difficult than image or text posting.
For storage, if we assume the format would be WebM at 1080p, 60fps and 20 minutes in length, it turns out to about 1GB. Even a cheap VPS instance usually offer 50GB of storage (with not too expensive storage upgrades).
So if its distributed evenly, we can host a good bit of videos (nothing compared to YouTube though).
I volunteer my trash can for Facebook, should do a decent job and it already has the smell to match, so we don't need to waste time implementing that feature