Whatever bike you get, 24 miles a day on paved roads means you would be best served with a good skinny road wheels/tires. Don't be convinced to go with a mountain bike or cross-bike width. Of all the weight saving materials, designs, etc there is nothing that compares to the difference in rolling resistance between a high psi skinny tire and a softer/wider tire.

You can choose a geometry that suites your favored posture and everybody has their own opinion, but remember what your friend Mike from BF.net told you - get skinny wheels/tires on your commuter.

Arm yourself with the very basic knowledge if you have not done so already;

1) Know how to change a tire and repair a flat
2) Know how to true a wheel (easier than it sounds)
3) know how to maintain your brake system from the levers through the cables and to the brakes.

Of course, there are many other things you could know on bicycle repair, that is the least you need to know.