For me, Lex has to be a very well known actor. Someone that makes the audience go damn I can't believe that got him for Lex.
Same for Jonathan, jor-el, and Perry.
Lois, superman, and jimmy can, and probably will be, relatively unknowns.
But imo, he really needs to pull a Donner and cast some modern day legends in those key supporting roles. ( lex, etc )
Just my preference but I'd go...
Lex - Matthew McConaughey or Edris Elba
Jonathan - Kurt Russell or Dennis Quaid
Jor-el - Robert Downey Jr or Jude law.
Perry- Denzel Washington or John Goodman