Sounds like you would run into E=mc^2 for your "lets just not have mass and stuff solves itself". The words "easily" here and there have a lot of work in front of them.

For the Alcubierre drive which also speculates on acquiring negative mass, the quote: "the energy requirements still generally require a Type III civilization on the Kardashev scale." says something about how well the word "easily" fits into such a solution.