I currently shoot wooden arrows, but I'd like to shoot carbons.  I shoot a 66" longbow 45# @ 28"  

Would I be spined correctly with .500 cut at 30 inches with 200-225 grains at the tip? Or should I go with a .400 spine?

Is the bow cut to center/past center/before center? Are you drawing 28"? More info would help. Odds are the 400 would be way stiff. The 500s may even be a tad stiff depending on the bow and your draw.

it's a maddog archery longbow.  i'm new to traditional shooting so i'm not quite sure about the center/past center/ etc

i'm drawing the full 28"

500s then

Id go with the .600 spine 1535 goldtips...

take your bow and shoot a shaft with no fletching on it,,, hold the bow perfectly verticle and without moving your head to "look" tell us what the back of the shaft does when you shoot it----> .500's will work as will heritage 150's and 90's it just depends on what you want for trajectory and weight.

my 45@28 PSA shoots un-weighted 90's but will also shot 150's with 225grain points..

so if you already have them do that or buy the ones you want and bare shaft one and we can walk you in from there.