Amazing! I paid $200 for my storage box and another $175 for used speakers. You are an excellent negotiator!
There are numerous web links on "how to install rear speakers in a boxster" on the web. You need to examine these carefully, but if I were you, I would not dismantle the passenger's side kick plate to do it. I ran my wires behind the passenger's seat under the carpet and tucked them under the center console to the head unit. Took five minutes and didn't require much unscrewing of any carpeted pieces.
You'll need to buy the brown (I think it's brown) plug from the dealership and wire it up so you can plug it into your CDR210 or CDR220... I assume you have one of these head units. If you have an aftermarket system, then you don't need a plug... just wire it up per the head unit's instructions.
Man, I am so happy for you to get all this for so little cash.