Coverage will largely depend on how the product is being applied. It's impossible for us to know how heavy or light each person will be applying the product. There are other variables like, porous surfaces, sharp bends/curves, holes or thin pieces like wheel spokes, etc. With all of that being said, here is what you can expect to cover with your touch up.
Touch up pens (chiseled nib applicator) are specifically design for the small jobs, i.e. rock chips and small scratches (think the size of a pencil eraser) - not large curb rash or scuffs from contact with a hard surface. The pen will usually cover all of the rock chips you can find on your vehicle with more to spare.
Touch up jars (brush applicator) are designed to handle the slightly larger chips and scratches (think the size of a quarter). The brush allows for more efficient spreading of the paint on these larger areas. It can also be used on smaller scratches and chips like the touch up pen. Many customers prefer the jar for its overall versatility.
Aerosol cans are designed to cover complete sections of a vehicle. You will be able to stretch the can much further if the surface is flat. An automotive bumper is a great example of this. Some autos have very simple bumper designs so you may only need 2-3 cans for adequate coverage. Some autos will have very intricate designs with cutouts and curves etc. A bumper like this may require 3-4 cans for full coverage.
In any case, if you are uncertain about coverage, the best thing to do is email a photo of what you are intending to paint and we'll do our best to recommend what to purchase. For coverage inquiries, please send an email with photos to firstname.lastname@example.org.