It depends on what kind of look you want and how long is your possible working distance.
I would rent at least 35mm and 50mm primes. For shooting human subjects, you don't always want the field of view that human eye sees. Humans remember the looks of other humans as they appear from a quite long distance (sorry I don't now find a source which says what the distance is). At short distance, the ears can look smaller than they appear from long distance.
Also, you may want to throw the background out of focus with background blur. Now, to achieve background blur, you can either use a wide aperture (but this decreases depth of field), or a long focal length (this can create background blur without too shallow depth of field).
Additionally, if you want to emphasize the human subject, 50mm would be good. If you want to emphasize the environment the human subject is in, and capture as much of the environment as possible, 35mm or 24mm would be good. However, your kit lens already has the 24mm aperture and background blur with 24mm is low and depth of field deep, so a faster aperture than your kit lens doesn't buy you really anything.
If you have a model for free, now is not the time to save on equipment and use only one focal length.
My suggestion is therefore:
- Use your kit lens for 24mm and shorter, use it wide open (which is probably around f/4)
- Rent a fast 35mm prime
- Rent a fast 50mm prime, at 10 meter distance the field of view is 4.8 m x 3.2 m which seems large enough, and you can get some beautiful background blur at this focal length and fast aperture
If you really really want to save on lens rental costs, I would pick the 50mm and use the kit lens for 35mm too. The reasoning being that background blur at 35mm is more difficult than at 50mm, so the fast aperture of a fast prime is more beneficial for 50mm prime than it is for 35mm prime. Furthermore, the aperture of the kit lens is slower at 50mm than it is at 35mm, so that too favors renting the 50mm over 35mm.
If you have the money to throw at lens rentals, consider renting an 85mm lens too. It is a focal length you can't achieve with your kit lens. The pictures will have narrow field of view and therefore have to be taken from a really long distance, but you may find it useful in some cases. A 85mm can achieve really good background blur, at the same time as having a deep enough depth of field.
Oh, and you may need an ND filter to use f/1.8 in sunlight, because the lowest ISO of your camera is probably ISO 100, and the fastest shutter speed is 1/4000 s.
Consider also lighting: powerful enough fill flash, diffuser, etc. can alter the lighting in ways you can't achieve with only sunlight.
Some cost estimates at lensrentals.com:
- Nikon 50mm f/1.8 costs $13 for 2 days
- Nikon 50mm f/1.4 costs $19 for 2 days
- Nikon 35mm f/1.8 costs $25 for 2 days
- Nikon 85mm f/1.8 costs $20 for 2 days
To me, it's clear that you want to rent at least the 50mm f/1.8 based on these because it's so cheap, if not going for the 50mm f/1.4!