Q: Can I get equipment or powers from other settings?
A: Sometimes. It should make sense in context, involve putting RP into it (so basically never at-application), and you should have relevant Advantage slots to devote to it. A typical robot shouldn't become a vampire for instance.
Q: If I buy a YT-1300 or Firefly-class starship, could they be better than the Millennium Falcon or Serenity?
A: Practically speaking this is impossible, as those ships would be Defining Advantages to the people who hold them. So a character who completely re-defined themselves with this equipment (which would be extremely odd) would still only be able to be around as good.