I have used Crutchfield
for the past 20+ years for all my audio/video gear. The folks there can get you started on the head unit to buy and the adapters to get it to interface with your Bose and steering controls. On the trim pieces fitting, since it's an Infiniti, that is a tough one. May want to have a professional shop install it in the event there is any fabrication done. As far as cost, the company above should be able to give you a cost for the headunit and adapters and they may be able to point you to a local installer as well.