Honestly, I think Starfield would be a *bad* setting to try and adapt to Starfinder. Starborn powers pretty explicitly exist on a different level above that of mere mortal humans, and completely separate from the 'standard' progression system. Trying to mix and match within a party would be like having a Pathfinder party where only *some* party members get to use the epic rules, and for pretty much the same reason. Realistically, you'd have to decide on either an 'all mortal' party, or an 'all Starborn' party. . . and even the latter would be hard to do using the Starfinder chassis.
Yeah, you could rejigger things, make space magic more common and less powerful, maybe make some other types of phlebotinum more potent and more available so there are more options. However, by the time you have a setting that is doable using Starfinder, you won't really be recognizably Starfield anymore. It'll just be Starfinder with some Starfield easter eggs/references.
( If I had to adapt Starfield to an RPG? I'd probably use Mutants & Masterminds or some similar superhero system. Starborn get to use full supers rules and higher power level, everyone else uses agent rules and PL. )
