For a standardish "head and shoulders" business portrait, there are a number of conventions you might want to consider. As ever, these are guidelines not rules and will probably make your images more conventional which may not be the look you are after.
For a "business portrait" you probably want an aspect ratio of between 1:1.6 to 1:1.2, depending on the layout of your website. I'm not sure I understand your constraints regarding image size, so you may have to work this out yourself. But if your maximum image height is 208 pixels you probably want to consider an image width between 132 and 175. The golden ratio of 1:1.61 is considered by some to be aesthetically pleasing.
You may also want to consider where you place the subject in the frame. Generally, you have the face centred in the frame with the eyes two-thirds of the way up the frame.
I would advice looking at different styles of lighting to see what suits you, and probably vary these depending on the subject. However, the one constant is that you will want off-camera lighting, whether it is natural or artificial. Lighting styles you may wish to investigate include:
You probably also want to ensure your subject have a twinkle in their eye or catchlight.
This is a stylistic choice in terms of colour, but you generally want to avoid a skin-toned background. Probably the most important thing when it comes to background is that it is neutral and uncluttered. Positioning your subject a good distance from the background massively improves portraits, whether the background be black or white. Portrait photography is much more difficult if you do not have sufficient room between the subject and background.
The "classic" portrait focal length is 80mm to 135mm on a 35mm camera, or 50mm to 85mm on a 1.6 crop sensor. If you choose a focal length that is much wider than that you risk distorting the subjects features.
Depth of field
As you are focusing on the head and shoulders, you probably want a narrowish depth of field to blur out uninteresting background details. Consider an aperture of f/2.8 - f/4. How much of the face you keep in focus is a matter of taste, but make sure you always focus on the eyes.
Unless your colleagues are exceptionally handsome, you might want to consider posing them on a slight angle to the camera.
It might take you awhile to get the subject comfortable enough with being photographed to start looking natural and comfortable, so take your time, chat and be prepared to take lots of shots you will delete later.