I'm not sure what you're trying to test, but you might be able to meet your need using a Meraki Dashboard Live Demo. If you don't already have a demo account, try this link: https://meraki.cisco.com/form/demo
With a live demo, you can create new networks in Meraki Dashboard and add whatever hardware you want. It's not a real network, but a fair amount of fake data will appear in dashboard and you will be able to make whatever configuration changes you need.
Of course, you can also work with your Meraki sales rep to get a reasonable amount of demo hardware.
I would like to test deploying a medium size network using APIs, but getting multiple Z3s just to prove the concept seems to be a rather bad idea 😉
I have recently commissioned a Z3C, for my own use. As I worked through the hassles (mostly to do with the LTE side of life), I noticed that each Z3C is in its own network, so here I have a Meraki MX network (Hengist.MyCorp.com) and then the Z3C network (Horsa.MyCorp.com). In the dashboard it quickly becomes second nature to switch between Hengist and Horsa, although with a 100 Z3Cs it could become tedious.
When the Z3C is connected to the Meraki MX network (via a MS port), as a network device it is on the Management VLAN, but that is my choice.
So far I like it, but I have yet to really tighten up on the security, that is coming. Slightly complicated by the need for an extended schema across three networks, because we are bit like an onion.
You could try registering for ECMS1 and use the free lab time to play with stuff.
If you use a demo dashboard I don't think you will get API access.
I think the best option would be to get a small set of demo hardware (try before you buy is the Meraki way!) then test as much as possible and then procure more hardware when your trial is done if it was a good fit. I think this is the best way to simulate real world use for customers and non-partners. If you are a partner there are other options.