Pacing wise I don’t think including the whole fight would work, I’m thinking more colour corrected flashes of Vader from the fan film saying Ben and other relevent dialogue like “come to me” etc when he touches the wayfinder. Could even get a shot of Kylo’s saber decapitating him in there.
Yes, it’d be more a ‘vanity vision’ for Kylo, it could mostly use the bits where Ben has the upper hand (maybe Vader’s force choke on him can stay, but not much else), as that’s what Kylo has in the opening raid. He gets stronger as the wayfinder calls to him/ultimately challenges him