I'd get a 3TB HDD for your videos, as they won't matter as much and will fill up space fast if they're high quality. The 1TB SSD should be fine for games for a while, assuming you don't install every single game you own.
I think the power thing is on about the connections from the PSU to the twin GPUs, as depending on how many extra things you have (maybe sound card?) you might fill up all the slots. I'd check where the sound card draws power from and count each individual slot.