From a network engineering standpoint this is how I would set up your internal network for the condos. Using the 10.0.0.0 private address block - 10.floor.unit.1-254 for each condo unit. If you are using managed switches and your own router - set each port on it's own vlan - if possible - this allows blocking off each tenant's unit from the others, which prevents DHCP clashes, virus spread, hacking etc... Set up the router with sub interfaces for each of the condo units and a simple acl blocking any 10.0.0.0 from incoming to each of the vlans. This allows access from the internet only, not from other tenants, unless they route back through the internet. Your router should support NAT as well for address translation.

And in other TANSTAFL news, the archive charges for each piece that you want to acquire. Even in death, he continues to adhere to the very philosophies he espoused in life. A tip of my hat to one of the Grand Masters of Science Fiction.