sgenius
Michal answered the license issue. Implementation wise, the first step for you? Step away from the IPAM console!
Okay, seriously, don't just start throwing things in there. From what you describe, there are some potential political / network administrative boundaries that exist. So before you start the mass import of data, be sure to know where those are FIRST. This directly affects how and at what boundaries you will permit users/groups for either RO acccess, Full admin access, etc.
Now, once you know where to lay out your boundaries, based upon your IP address structure - NOW you start laying out things in IPAM. If you start with the blank template provided, everyone gets access starting at the top. Small areas, this is okay. Larger areas, it can get cumbersome really quickly.
It can be somewhat tedious to manage the alignment of your logical IP address structure with the sometimes illogical manner of how the network is taken care of, but a few minutes planning now will save you headaches later.