Re: Creating two networks
I would suggest you would be needing a firewall somewhere between your more public bits of cafe kit, and the private office stuff.
Most routers will allow you to also set fixed IPs to PCs, but for real security you do want the office to be on a separate subnet.
Basic wiring would probably be:
modem <> wireless router <~~> internet cafe
and wireless router <> firewall and/or 2nd router (set with forwarding to wireless router) <> office
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