Also forgot the aperture advice. Avoid shooting wide open when possible. The 400 II may work ok at 2.8 but usually a click or two down helps the sharpness quite a bit. I would avoid f8 or higher due to diffraction. Also try to keep your shutter speed at 1/1000 or faster for flight shots. I actually try for 1/2000 or faster. ISO noise is generally not a problem on the 1dx up to iso 3200 so would definately use that for flight shots and the 1d IV for statics where you can keep the ISO down to under 800.
Thank you for good tips, on both aperture/shutter/iso, and also for the considerations on teleconverters and lenses. I have to see what I can borrow, but when it comes to these really expensive lenses like the 400 I have to ask a good while in advance I do not have the 1.4 TC, but a friend of mine have it and I can certainly borrow it from him.
I am very thrilled about this and have been waiting for the season since I got the gift in May last year
I have actually not seen the interior of the hut, so I am not sure about the use of tri or monopod options, with or without a Gimbal... I better send them a mail.