Yes, typically you'd need to create a scene for an idea, with the scenario editor you can do most of the work. You might want to do some scripting to make the scene more lively. Then you need to create camera paths (again scenario editor) and finally render the thing.
I don't see an issue with uploading videos about random topics to the play0ad youtube account if they are of similar quality as the release videos, whether short or long. Civ intros sounds like a good idea. Doing a few of them is also good practice for when the next release video is due in roughly 6 months.
Not necessarily recruiting as an official team member but surly as a contributor. I for one contributed to many open source projects, hardly any of them in an official role and don't see a reason not to do so in the future. Less commitment but still able to improve what I already use and value. For some that is plenty satisfying already.