I work with 7D, T3i, A7s, C100 and RED Scarlet mounted on Ronin-M mounted on DJI S900, Inspire 1 and Phantom 2, Phantom 3 and Phantom 4. Adobe Creative Cloud CC (Premier Pro CC, After Effects CC).
Neither, both are a waste of money for the power you're getting.
I would get an SSD for sure. Cloning won't speed you up at all and that's RAID 1. RAID 0 is what you won't for speed (but not redundancy) as it will stripe the data.
Perfectly usable to me. Your instance might be corrupt or it could be some driver corruption too.
Building the drone is easy. Trusting the drone to stay in the sky is impossible. Especially when it doesn't half the time for random reasons. Then don't even think about trying to live stream video back. You'll spend hundreds of dollars and hours splicing connectors for different image transmission systems and connectors. Not worth it. Built my own 6 prop and flew a DSLR and RED on it. Not worth it...
I agree proxy will be the only way to go for this macbook...
Nobody will ever seen UHD? You are long mistaken my friend. 4k Monitors just priced dropped to under 300.