Also does the af area have any affect on the ae-lock?
It shouldn't. I'm 99% sure about that. As long as the you have the subject focused then lock exposure, you should be okay.
From what I recall if you are in Single Servo AF mode and recompose, changing camera to subject distance you will be out of focus; just keep the AE-Lock slid over and adjust focus by releasing and re-depressing the shutter release to activate focus. In continuous servo, you should be okay; the camera will refocus the camera to subject distance changes. (I know this is how my N70 works.) Anthony