Network Situation Advanced Networking (Office)?

This is fairly straightforward stuff really: to be honest I wouldn't trust a professional that it caused difficulties for. Pop each client and the shared resources on their own subnets - 8 in total. Hook them all into the same router and configure access control lists that prohibit routing between client subnets. A basic enterprise router will do this no problem - say a Cisco 2600 you can pick up on ebay for perhaps $30. You'll also need a managed switch to break out the individual subnets to access ports from a trunk port, since you won't find a router with eight separate ethernet interfaces. Again, perhaps $30 on ebay.

As for the wireless the cheapest way would probably be to simply equip each subnet with its own WAP. A more elegant way would put the wireless into the router - again, enterprise grade wireless routers can handle multiple subnets and SSIDs over the wireless interface. I have a Cisco 1801W here that would handle that with ease, but you can probably go a bit more basic than that - an 877W _should_ be able to handle it.

Not possible. The landlord does not typically provide the network for the tenant; it's the tenant's responsibility.