Hi Condor,
You need the Euro Motor Speed install kit, you can get it from Loi Trieu euromotorspeed@gmail.com or call 727.455.6580 This kit allows you to use the CDR wiring bundle with no changes whatsoever, it's truly plug & play and comes with the brackets to insert a double DIN head unit into the opening in your dash and includes an awesome bezel. If memory serves the kit costs $250 and Loi truly provides world class customer service.
You can plug your antenna into the Pioneer unit, no brainer. The amp in your frunk will drive all your current speakers same as it does now, if you want to replace the amp then the new one will drive all the speakers easily. Feel free to email jeff.logan2010@gmail.com or call me if you need more info 503-647-7654 Best, Jeff