How i began with birds in flight photography,is go down to the where you find the bigger birds, ie gulls, ducks, swans etc, harbours, rivers are good places, and if you can take someone else with you to start accompanied with a bag of bread! (although at places like this gulls dont need much tempting!) get the other person to throw the bread upwards and get the gulls flying, you'l find the bigger birds alot easier to focus on as they are slower and more methodical in flight than small birds,and they make good subjects to practise panning techniques on.
I find this sort of photographing easier hand holding my camera, but after a few attempts and the pictures get better its kind of addictive!
Your lense sounds fine and Barrys settings are great, i use Aperatue priority mode (my preference) usually ISO 200 depending on light and if using the 100-400L i keep between 250 & 300mm, and again individual prefence is on motion blur to wings etc, i try and work between Sspeeds of 1/250 and 1/700, and on very dull days may go up to 1/1000.
