I think Mars is a really crappy place to build a space colony. The gravity and atmosphere are pretty useless. You need to make gravity and air, so you might as well just do that in space. Earth orbit seems like a comfortable distance from Sol, in terms of energy you can collect with existing technology. Capture a few comets for gases and asteroids for metals, and you are set.

Build a spinning ring to live in and you have 1 G. Build bigger rings as you get more people. Photovoltaic arrays don't spin so they can point at the sun 24/7.