I watched your episode zero (taken from the Clone Wars series’ Bad Batch arc) and it’s all you could hope for. The original content isn’t particularly strong, but you’ve cut it exactly right, trimming the fat and keeping the focus on the Bad Batch characters. It worked as an example Bad Batch mission (introducing them all through the lens of Rex, and with Echo as the emotional core), and I was glad you completely removed the final episode for pacing and focus, using only its ending.

It works far better as an episode of the Bad Batch than it did as a Clone Wars episode, so I was glad you cut the Anakin/Padmé content (especially since I still used just those scenes in my TCW:Refocused edit elsewhere), and the Anakin/Mace content (which wasn’t very additive, except for the scene of Anakin killing Trench, which I also would have cut from this or TCW:R anyway as it’s too similar to other things we’ve seen in TCW, and Trench doesn’t need to be a major villain.

I have only three minor ideas you might want to consider:

Opening with a subtitle saying “Shortly before the end of the Clone Wars” or similar, to just clarify when this is set if you’re picking the show up after TCW/ROTS (which I reckon anyone should).
Since I’m a big fan of skipping the Citadel arc (as it’s just not very strong, despite Tarkin’s appearance and Echo’s death), and it’d be a while since the viewer had watched that anyway if they were watching in chronological order, I would look for an opportunity to include Echo’s death as a very brief flashback - perhaps during the scene you cut with Rex pondering over a helmet. I’m mainly asking this because it’d help me personally - some do want Citadel included in TCW:R, just for that scene alone, but it’s so throwaway - but it could add value to this episode since this is the first point in the overarching story when it becomes relevant, and you do have a good scene to embed it in.
This is a bit of a longer shot, but you could end this episode on TBB#1’s opening, the newsreel (perhaps without the newscaster’s narration), to effectively bring us up out of this episode’s extended flashback and back up to speed. That’d get that out of the way, allowing TBB#1 to begin on the actual drama, not an extended intro.