1. Wrong: If I was able to eliminate all Saturday classes, I'm not sure I would.
Better: If I were able to eliminate all Saturday classes, I'm not sure I would.
Also better: If I could eliminate all Saturday classes, I'm not sure I would.
Explanation: The introductory if makes clear that what follows is hypothetical.
2. Wrong: If Robbie was in charge of the world, music would come out of all sidewalk vents.
Better: If Robbie were in charge of the world, music would come out of all sidewalk vents.
Explanation: Starting a sentence with if shows that the idea following is contrary to fact.
3. Wrong: I wouldn't recommend eating a handful of habanero peppers, even if you can.
Better: I wouldn't recommend eating a handful of habanero peppers, even if you could.
Explanation: The sentence shows that the person being addressed may not be able to eat the peppers.
4. Wrong: I wish my family and I have a million dollars.
Better: I wish my family and I had a million dollars.
Explanation: The wish shows that the family does not have a million dollars.
5. Wrong: Harley and Justice insist that Cam thinks this proposal through.
Better: Harley and Justice insist that Cam think this proposal through.
Explanation: What is insisted is a command, so it belongs in the subjunctive.