Diamond stones will cut VERY fast compared to arkensas/ceramic/whatever, I can give you that much...
I don't see why you need a lansky stone between those two grits, for knives, I usually start with 120 if I'm rebeveling and jump all the way to 600, skipping 280. Even if you're using tool steels at high hardnesses, it's kinda unneccessary.
Freehand, you've got A LOT to chose from. But I wouldn't spend too much on your lansky rig. I've got one with 5 stones (120/280/600/1000/2000), which I consider about optimal. But I'm trying to get into freehand, as I usually use my lansky stones in that fasion anyway (freehand). You can get a keen edge much faster and without reprofiling with freehand sharpening.