On a more practical note, you really need to use the black ones as they can take the sun. The natural plastic color ones will only make it a few months before the sun would kill them. Heck I was thinking that those ones that Tim was using when he put it up weren't going to stand the test of time, but they have.
Your standard 7 inch 40# tie will do just fine. It's only a 2 inch pole, and from the looks of the picture, my 2 year old ties held up better then the flag.