you will be gimped speed
Your signal already goes through several routers to go from the origin, to your ISP, to you. Each router hop only adds a couple milliseconds of latency
like a hub.
Hubs don't do any processing of packets like a router or switch does, they just blindly pass the signal to all other ports connected, so they really don't add any latency
because its more likely that ethernet cable is already coming from one.
Of course, but if he wants internet access on more than one device there's not much else he can do.
He can either buy a wireless router, or an independant router/switch + a WAP