Multiple systems become unwanted baggage, and will quickly become ignored by your subordinates. After World Domination is achieved, I am going to create a new task force. Capture and torture will not be discouraged. The linguist that you hire will be given the task of devising an entirely new language. You may or may not choose to utilize a new alphabet. I encourage you to do so since it adds a secondary level of secrecy.
Powers can be blocked or countered leaving yourself defenseless. Know how to use high and low tech weapons, and always keep some on your person. Secret, and unknown from even your closest advisors.
Do Not Care Packages
Destroy france, turn Iraq into glass, flood Australia, all amazing events, but you know they will happen if the Overlord says it is going to happen. For most people, when they threaten to destroy the world, we would simply laugh at them, and continue on with what we are doing. You do not want any possibility of it happening. Even if the individual had zero access and zero knowledge, you still want to prevent the other guy from having a top notch employee. You know they are top notch because otherwise, you would not have hired them.