I love Yoda's quote: "Size matters not."
I've observed that the most important thing in a Jedi/Sith is their faith in the force. Sure - midichlorians help, but in the end what matters is how much you trust the force. If you can lift a rock with the force, then you should be able to lift a planet (at least that's my interpretation).
Well, I doubt someone could lift a planet but the analogy is good. Size does not matter. But to use the Force requires a number of factors:
1. Midichlorians... Obviously. The more you have the greater your connection to the Force.
2. Dedication to your path... To use the Force requires dedication to your path, Light or Dark. Your dedication to the Light or Dark Side can also determine your ability to command the power of the side you have chosen.
3. Willpower... Where there's a will, there's a way. Great feats with the Force requires a strong willpower. The will of the Jedi can decide what he can do. Can he move the rock? Should he will it, then yes.
Midichlorians are the most important part of this trifecta, but the trfiecta forms a circle. Dedication and willpower revolve around Midichlorians, but Midichlorians can mean nothing without the proper training and the other two parts of our trifecta.