Yes it can be used wirelessly. That's how my setup works. As far as the wireless networks strength, do you mean available bandwidth on the wireless network? Yeah it would lower available bandwidth, but most likely any G or N network would be faster than your broadband connection anyway, so your concern should be more about how much it will bog down your home
Internet service. I use my roku box and stream HD Netflix all the time while using sometimes using two other computers all on the same wireless network and have no problems on my 15 down/2 up connection.