Your right about the amber, I read the email that is provided in the post above that is said to be from bells directly. They say the Amber is the one to use.
This is my first attempt at this so I'm no authority on the process. I'm sure someone on here has much more experience than me.
You can calculate your starter size using this calculator
But basically the process is the same as building any liquid yeast starter. Build a small low gravity wort, add the dregs from a few bottles. Let that ferment out. Cold crash and decant off wort. Restart the process. Then continue until you have the size starter you require.
anyone with more experience that would like to chime in would be greatly appreciated.