Hardware advice for machine vision project
The things you can control with the camera selection are:


Resolution
Sensor size
Sensitivity
Frame rate


The things you can control with the lens selection are:


Focal length
Minimum depth-of-field (DoF)
Field of view (FoV)
Minimum aperture
Zoom functionality


Each of these interact with each other so it is often difficult to find the right trade off.

The sensor size and resolution are usually related. For example, it is hard to find sensors with resolution above 1024 * 1200 in a 1/3" sensor. 

The resolution and thus sensor size will dictate what lenses can be used with the camera, then combined with the FoV of the lens will dictate how many pixels the face covers in the image. 

First decide how far off-centre the face can move. That will guide you minimum FoV. The work out how far away the face can be, and how many pixels wide it must cover. Using the average width of a face, the FoV angle, and the depth you can work out the minimum resolution you need. 

Using the minimum resolution and DoF, choose a camera and lens combination. Pay close attention to the maximum sensor size the lens can accomodate, and note that the FoV changes with the sensor size.

The DoF is a function of the lens focal length and the aperture. To increase the DoF you have to reduce the aperture. E.g. f/1.8 is wide open, f/22 is almost closed. A smaller aperture will let less light in, and thus the camera exposure and gain will need to be increased. Choosing a camera with high sensitivity will allow you to get better images with less gain increase while keeping the exposure short enough to not be blurry.

Motor driven zoom lenses are available.

Near-IR is possible with many camera manufacturers, as they actually have to put in a filter to block IR, so making a near-IR one is easy - just take the filter out.

But probably my best piece of advice is to contact the camera manufacturer and ask them. They have people that will take your specifications and recommend a camera / lens pair for you. Personally, I have used Point Grey cameras.