Student or Learner
1-Are you for or against my plan?
2-Are you with or against my plan?
For or with?
Agree, but "Are you with me" means the same thing. Are you in agreement with me? Are you going to join me in my efforts to get this done? (For my plan, with me.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.