If Japan has 16 spots (fairly guaranteed, NHK = 3, Rostelecom = 3 (you scratch my back and I'll scratch yours between Russia and Japan, they both want as many entries as possible, and are very close to the limit of 18), CoC and IDF = 3, no axe to grind, they just want as many good skaters as possible, SA + SC = 2 each), then I would expect the following
Satoko Miyahara - 2 spots (guaranteed 2)
Wakaba Higuchi - 2 spots (guaranteed 2)
Kaori Sakamoto - 2 spots (guaranteed 1 + invite based on very high Seasons Best)
Mai Mihara - 2 spots (guaranteed 1 + invite based on very high Seasons Best)
Marin Honda - 2 spots (guaranteed 1 + invite based on high Seasons Best/big name)
Mako Yamashita - 2 spots (guaranteed 1 via Seasons Best + invite based on high Seasons Best/World Junior medal, no need for NHK Host Pick)
Yura Matsuda - 1 spot (so far) - guaranteed 1 via Seasons Best
Rika Hongo - 1 spot (so far) - guaranteed 1 via World Standing
Running total 14
NHK Host Pick - Rika Kihira (most likely)
That leaves 1 invite between the 2 Rika's, Yuna Shiraiwa and Yura Matusda, but I imagine it would most likely be either Rika H based on her big/well known name, or Rika K based on her potential/3As.
If Japan has 17 spots (Russia had 17 last year) then it'll be 2 invites between the 4, and if 18 (it would mean 3 Japanese, and I'm sure 3 Russians, at each GP), then it would be 3. I would imagine the ‘batting order’ would be Rika H/K, then either Yura or Yuna if there happens to be 18 spots.
I also wouldn't rule out 3 at each GP. If you don’t get this it would mean bypassing skaters with Seasons Bests in the high 180s/low 190s in favour of those with SBs of 175 or lower - that's the cut-off point if you take guaranteed spots, Host Picks, and assume all invites are in Seasons Best order.
Hence it'll be interesting to see what happens this year, and in future ones. The Japanese and Russians are getting stronger all the time - there's 18 out of the top 24, and 24 out of the top 32 Seasons Bests this year that are either Russian or Japanese, and it doesn't look as if it's going to change any time soon. Hence it’ll be interesting to see what the ISU’s and other GPs attitude to this will be. Will they accept it, or will they be looking to still get as even a split as possible, with other countries, often little ones, getting representation.