Like my respected colleague Ernie, who has a background in this, I am wondering why you, as an admitted novice, have been assigned this task instead of hiring a professional. I would guess it is a small business with a limited budget and hopefully not too many employees. If that is so, all we can do is try to make this work for you as best we can.
As my colleagues have alluded to, this is a limiting budget and for any decent lens you will not be looking at a significant lighting rig. Personally, as @KVBarkely said, a good source of indirect natural light is best to give you a soft, even light to keep things simple, and so you don't need lighting gear. I recently took a series of headshots for a professional group of scientists as a favour as they had NO budget, and these are some samples of the results using that lighting technique.
Things of note:
1. I chose a plain, neutral background (I used a mid-gray as it was in the foyer of their building and that reflectance of background will give a good exposure reading ), I was looking for a consistent background - you don't want lots of significant changes in colour or clutter. The indirect, soft light reduced facial shadows, stops them squinting and, by reducing wrinkles, makes people look younger (which you will find older folks like).
2. In my case I was using a full-frame camera with a focal length between 70-130mm - in your case, because you have a crop-sensor camera, which has a magnifying effect, you would select something in the range of 50-80mm.
3. I had the subjects about 3m (10ft) away from the wall to keep it out of focus, and avoid wall shadows, and shot with a focal range in the f/4 -f/8 range. You would likely shoot from f/2-f/4.
4, I was using auto ISO but limited to 3200.
5. Shoot in both JPG and RAW file formats, both at maximum resolution
6. Make sure you have Face and Eye tracking for people turned on in the camera and, if you are shooting hand-held that image stabilization is on. Also, look through the viewfinder not the LCD and hold the camera properly:
So, a lens as has been suggested one of the following, which you can get from the Canon Refurbished Lens Store:
a) $160 for a 50mm would give you an equivalent focal length for your camera of 80mm:
Shop Canon Refurbished RF50mm F1.8 STM | Canon U.S.A, Inc.
b) $490 for RF 80mm f/2 Macro lens - an equivalent FL of 135mm, also excellent for portrait work and a shade under budget:
Shop Canon Refurbished RF85mm F2 Macro IS STM | Canon U.S.A., Inc.
In both cases you need to compose so that you get roughly the torso or bust in view, make sure the camera is level and get the subject to look directly at the lens. I often suggest they close their eyes, and I give them a countdown to open them, at which point I take the shot - which makes the pupils of the eyes larger.
Men often prefer to be slightly oblique to the camera (although not always depending on light) women prefer to face on - it reduces wrinkles.
Beware of reflections or distortions from glasses, so position your subject carefully to avoid that.
Beforehand, tell everyone what the procedure is, when and where to go, and that everyone should be clean, and dressed according to company policy - tell them this is how they will be seen by their clients. If there are a lot of people, you may want to give different groups specific time slots and be prepared to adapt and negotiate - business will go on even when you are shooting.
When taking the images, if you can, take a few moments to talk to the person about their job, hobbies or whatever to make them relax it makes a difference to the muscles of the face and neck. I always assure them that there will be no images published without their approval, it takes away some of the stress and that I can re-shoot if they don't like the results.
Take several images, and I usually do one slightly facing left, then centre, then slightly right: not just one. Everyone has a preferred side.
You will need to do some post processing and if you have a art/marketing department they will likely have software and the skills to complete the image process. Otherwise you may want to become acquainted with Digital Photo Professional 4, which is a free program with your camera and is used to process images.
Recon the location and find someone to practise with before the actual shoot to make sure you are not in learning mode.
