Why would fusion power result in "enourmous abundance" of usable energy? A fusion power plant would not run on magic, it is an extremely complex, very expensive high-tech system which requires human oversight, maintainance, and fuel.
Yep - our already built fission plants are starting to go out of business because the power they produce is too expensive. I don't think we should bank on fusion plants being incredibly inexpensive to operate.
Sure but then we can just use the energy to suck all the co2 out of the atmosphere and blow it out into solar orbit or something. There are better materials to use for making plastics with infinite energy, although I'm probably not qualified to make that statement.