Aftermarket Nav Questions

Has anyone installed an aftermarket nav system? I'm considering installing a decent Pioneer double din unit, but a few things are holding me back:

• I'm unsure about which dash kit I would use - Metra or Schoshe. Has anyone used either one? Pros? Cons?
• Is there a good way to retain the usb and aux inputs in the armrest?
• Is it necessary to use an additional nav antenna, or is it possible to use the one already in the car?

Thanks much for any input.


Tom