1) I've had better luck with Kenwood units than with Pioneer so that's all I can say there.
2) You can use an adapter to use the OEM antenna if you have one but you cannot use the OEM tuner and would have to buy a tuner.
SiriusXM SXV300V1 Tuner Enjoy SiriusXM satellite radio with your compatible aftermarket or factory radio (subscription sold separately by SiriusXM) at Crutchfield
To add, I'd use an iDatalink Maestro for the interface.
Edit: The Maestro may allow you to use the OEM SAT tuner. I'm not sure.