Ok, let's get a few things in order...
Your Temp should be TDC (top dead center) when at proper operating temp. If your temp never rose to that level, your thermostat was bad and stuck open. So when your car is now actually getting up to temp, it's not overheating, it is finally getting up to temp.
It does now sound like you have cleared the vapor lock from your block when you opened up and replaced the water pump. Regardless of whether you are running a 6 cyl or 4 cyl radiator, proper cooling system bleeding is required to ensure no bubbles remain... See this DIY -
http://www.318ti.org/forum/showthread.php?t=27983 Why you blew the top radiator hose and why you may have a tank leak are most likely separate topics...