Hello Again. I am looking for some more advice on honing

I am currently hone my TI 6/8 Throatcutter (love it) on the following stones...

Naniwa 1k,5k,8k,12k Superstones.

I also purchased a Naniwa 400 grit that i would use for kitchen knives to compliment the Edge Logic 1/3k combination stone. However, Could a guy use the 400 to set a bevel on a straight razor? Or is it too course for starting. I worry about scratching up my spine with it.

My next question has to do with the swarf. Not so much the swarf, but the particles that get inpregnated in the stone itself as one is honing. I see this often in the higher grit stones. Does that actually diminish the sharpening effect of the stone? Sometimes a quick rub with the thumb will remove the blackness that is in the stone.

Thanks in advance for the Replies, This is a great site for advice