I use velcro to hold it and it works fine. Make sure the one you get is water proof or you get a case to protect it.
Actually you can glance down when it's where the OP suggested and you can still keep an eye on what's strait ahead pretty good.On top of the guages behind the windshield would be better for this,but I think it's better than the handlebar mount because you're looking sideways at it.JMHOI would consider to place the GPS elsewhere. You will be looking down so much. Place it somewhere You can keep your head up.
As for cables, it all depends what you need. Mine came with the 12v accessory cable, but did not come with mini plug cable to connect the audio.