I don't know how much the Cubs can get from Japan market. But, if the Cubs sign both Imai and Okamoto, they would be the first MLB team with four Japanese players. If I remember correctly, Yomiuri Giants, Okamoto's team, is the most popular team in Japan. And, he was the best hitter they had for a while. That should be able to get a lot of sponsors from Japan, I would think. If that's the case, they might be able to make more profit, even if they go over the LT line. The posting fee is another issue, though.
That said, signing Okamoto (or Bregman) doesn't make much sense, unless they trade Shaw or Nico, which I don't like. Even if they trade Nico, Bregman would be too expensive and too long for the Cubs. Resigning Tucker would make more sense than Bregman, if Tucker can't get a long term deal. BTW. I don't think Okamoto can be a good 3B. He's either 1B, LF or DH. So, yeah, Okamoto isn't a good fit for the Cubs.
If they don't get Imai, I have a feeling that they don't get any SP, unless a good trade shows up. I don't think Imai is going to be really expensive. I could be totally wrong, of course, but he's gonna sign something like 4~5yr, $20M AAV or less. If the Cubs doesn't offer him that kind of contract, they probably wouldn't get Gallen, either.
Anyway, we'll know very soon.