Ok so I'm putting all my movies on a 1TB hard drive and have a question. I know what the iUSB does, but can I stream them to my ipad and then stream to my Apple TV using mirroring or would my hdmi cable from ipad to tv be better?

A cable would likely work better in the since it would be more reliable. I've done it both ways (not using the iUSB but another device)....sometimes the wireless doesn't always work well. IME.