1) if stock HU does not have AUX-in...hard wire FM Modulator is your answer.
This thing will be hardwire behind your HU so everything is consealed.
It plugs between your antenna and your HU and draws 12v supply from a 12v source inside your cabin..
2) I feel..(my opinion) 600mhz is too slow for my taste. But depending on what you're planning to do with it. It might just fit the job.
3) there is a .pdf diagram on how to wire the Opus. You'll have to do a search on it. I'm too lazy to do it for u.