q1: Yes, you can pretty much request everything you want from the smallest to the biggest box. You start at this URL:
https://meraki.cisco.com/form/trial
q2: Yes you will have full administrative access. In fact you will have to create your own Organization (a Meraki Dashboard concept) to put the trial kit into.
q3: Only Systems Manager has a user limit. Other devices are only limited by the number of ports (such as a 24 port switch) or CPU power (don't try and put 1,000 users on an MX65 and hope to get a good trial).
q4: There is no restrictions in the demo environment to do with trial gear.
q5: You will most likely be setting up the environment yourself. You should know the normal things, IP addresses, etc.