This sounds really cool! I’ve commented on a “Star Wars Epilogue” here before, so I’d be happy to help out in any way possible.

IMO - the best way to preserve the Vader twist is to use The Clone Wars. I know this isn’t ideal - it uses animation! But if you adapted Season 7, we could still tell the story of Anakin being a hero, just without the turn. If you have Anakin turn in his first outing, I don’t think people will like him, and all it will do is give hints that Luke’s father isn’t as good as he seems. Whereas TCW reinforces the twist well. You’d feel sad not just for Luke’s father but for Anakin Skywalker, Clone Wars hero.

Plus it all links up perfectly to Order 66.