But rather than have the ultrasonic sensor directly on it, id like to have it set up remotely with an ov7670 camera, and controlled through an uno or mini, then communicate to the mega using either a bluetooth sensor or esp8266 wifi sensor, again depending on pin limitations (and effectiveness of one over the other, potentially).
Do I understand that correctly, you want to replace the ultrasonic sensor by camera? Does that mean you think that an Arduino is able to detect motion on a camera picture? it doesn't. It doesn't have enough memory to keep a complete picture in RAM (so it cannot compare multiple pictures to detect changes) and it needs several seconds to read out one picture from the camera. Forget that setup.
If you want to do a motion detection by camera, use a system like the Raspberry Pi, which has the memory and computing resources needed to do such a job.