Given the budget the 70-200mm f/4 is your best and only option for what you want to do, but if you slightly stretch that you can get the Tamron or Sigma 70-200mm f/2.8 non-IS and will be much better than the f/4 (twice as much light) but the focus is not as fast or consistant as Canon. For about a grand you can get a used canon 70-200mm f/2.8 non-IS and get fast acurate AF with the brighter aperture.

When refering to crop bodies it means that the senor is 60% smaller than Full Frame (which is the same size as 35mm film). Because of this you will gather 60% or 1.3 stops less light, 60% or 1.3 stops more DOF, 60% or 1.6x longer effective focal length and 60% or 1.3 stops worst noise (because of 60% less light) assuming the same sensor technology. You will also crop away lens resolution so depending on the lens it can be marginal to very noticible.

Hopefully that will be enough to get you confused....

Cheers,
John.