It sounds like you want a NAS (networked attached storage) for your files.
NAS, Network Attached Storage, Home Sharing, Network Storage, Private Cloud - Newegg.com
You'd want a N/AC, Gigabit wireless router, but anywhere you could hardwire you should.
Wireless Routers, Best Wireless Network Routers - Newegg.com
For the router settings you'd want to change your SSID to something unique, then use a WPA2-AES password for router security. You could use MAC filtering for even better security, but that would be a hassle for guests...SO...
A couple off questions/issues:
Did you want/need to access the NAS off-site/away from home? Why do guests need access to the NAS or do they?