I'm going to guess no. Video would exponentially increase the bandwidth and data storage requirements of instances when these instances already can barely handle their user load and static images being uploaded.

Use an external hosting service as much as you can. Linking directly to something actually designed to distribute the load, like PeerTube, is vastly more efficient than expecting Lemmy instances to handle it.

It's already supported, but disabled by default (for good reasons).

As far as I know, yes, but nothing is done regarding that currently cuz there are more important matters to be handled/implemented, like being able to follow users and a s*itload of other bugfixes and smaller features.