After installing a new radiator, do you have to "bleed" the coolant?
 

What does that even entail?
What type of coolant should I put? How much?

Oh yes. Failure to properly bleed off all the air from your coolant lines can cause air pockets that result in a cracked head or failed waterpump. A Boxster is far more difficult to do than a typical Chevy/Toyota motor. The best way is with a vacuum bleeder. Here is the Pedro simplified method that I used.

Install 3rd Radiator & Coolant System Bleeding Instructions

Thanks, that helped me tremediously

Yes, do bleed the coolant. I did those exact procedures when I had to replace a cracked radiator. You may want to have an assistant handy; I got a helper to hold the rpms for me.