Yes, videos would be especially helpful to show to players who know mainly proprietary games "This FLOSS game is cool, too".
And yes, they should not be too long. I think 5 minutes are maximum. But maybe even shorter maximum.
They could be similar to a "Let's play".
A central point would be cool. Could be a website (maybe libregamewiki), could be a planet or a mastodon account. Maybe a website AND a planet/channel.
Greetings
Peter