I'm new on this forum, as I'm planning something similar for this summer, but I can share with you my thoughts on the camera setup.
Most of the lenses from Rokinon are manual focus, but that's just a better thing for you.
As you're using a wide ange lens, and you're taking pictures to a quiet high altitude, you have just to lock the focus on the lens to infinity, with that you can also avoid lot of problems related with 'point to shoot focus'. I'll not recommend a fisheye lens (just to let you know, rokinon has a valid option also for a fisheye, that doesn't cost 1000$), that's a personal opinion, maybe, as you're shoot with an APS-C camera, check the rokinon 10mm f2.8, I used to have it before.
Also, for the exposure setup, I suggest to lock the aperture at around f5.6-8 max, and let the iso stay below 1600 and the shutter speed below 1/320. I know you're flying at 5m/s, and everything's moving, but with a wide lens, you don't need a so fast shutter. For sure, keeping the aperture as said before, will help you with sharpness.
(Source: photography is my full-time hobby)
Let me know what you think