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I would go with galactic heroes, cheap, easy to play, plenty of star wars type powers and very adaptable.
cool idea I'm too invested in my collection but I do remember seeing some really nice pics online of galactic hero figs.
A Wing and Jango Slave 1
Seconded - Fistful of Lead: Galactic Heroes is the set we use for Star Wars games.
If it's at a few models per person sort of level your looking for mutants and death Ray guns is what id recommend. That ruleset can be modded to do most anything. If you go on the song of blades and heroes Facebook group and ask how to make it into 54mm I'm sure they'd help make it work for you.
Who makes that Stormtrooper standing by the AT-ST's leg? I don't recognize him.