Well, with 5 ID's, put 2 to your mobile reserve. 2 at Bihoro and 1 at Kushiro. You'll have to hope you can hold at both places until you can reinforce. I'd move another 500 IJA LB to Hokkaido so that you can hit his troops at his beachheads along with another 500 IJA fighters for escort. This is above what you have moved to attack his naval landing force.
Other than that, keep moving ID's to the area. You've got 8 identified, that's about 2500AV. On defense, that's not bad. But if you have to retake a base, you'll need a lot more. I'd get 7 more moving in that direction. I know its a lot and hard to find, but you cannot lose Hokkaido. Holding the line in SE Asia or DEI is meaningless if you lose Hokkaido, right?
Best guess, if he is coming for Hokkaido, and your last screenshot does not indicate otherwise so plan for it, then he will come with ~10ID + support.
Your biggest decision is what do you attack with your naval aviation? What is your plan there? The landing force or the Death Star?