Ok so I attempted my first color separation the japanese style today. The image I am doing is a field in the snow and doesn't have a traditional keyblock. But I needed to know where the edge of the image was and the registration. This is the separation I didn't end up using. And you can see there are some pretty bad printing issues here. Overinked and underinked all at once. Also I think the pigment was too light. I was grinding solid sumi ink. It was the only decent black ink I could find in my house and I don't think I ground it enough.

At least all my blades of grass printed. I was getting worried about that.
This print is only 2 blocks
I was able to cut the outlines of the color shapes and the kento registration before the paper started peeling up. So I am just going to sketch directly onto the wood for the details in my color block.
Oh and this is the nori paste I found in my art supply store.
It was $2 and is a bit stickier than what you describe but I was able to water it down. But it didn't have the hold to keep the separation glued down. I had a lot of difficulty laying the separation down. I assumed you have to glue it wet otherwise the paper would change size and registration would be off.