Another E5/EM5 user here. Unfortunately I don't have much advice for most of your questions... : )
The Sd card should be fine. A smaller flash would make sense but I haven't tried the new Oly one. I've used my big fl50r around the house and it's pretty silly on such a small camera. There might be better third party deals out there if you look (compared to the new Oly flash).
The batteries I don't know. I stick with the Oly ones, but others seem fine with the knock-offs.
You already hit on the main thing with color, to turn the warm toning off. You will notice the colors look somewhat cool then and that might be just what you want. I've downloaded the Huelight profiles for Lightroom which are supposed to (I think) give something approximating the Oly look. I like them, but it's far from a "one-click" affair. Anyway, the EM5 makes great jpegs if you want to stick to that, or use Viewer.