Something worth keeping in mind:
I've been gathering up a lot of information about the Pacific War and most of the threads I've seen at some point mention how the Japanese were on a tight schedule and how Japanese needed everything to go just right. I'm wondering what was the Japanese contingency if their coup d'main turned sluggish. Like had the invasions of Malaya and Philippines bogged down quickly and the Japanese suffered high casualties, what was Japan's plan? Just send in more troops and if so where would these troops come from? Also how would the bogged down campaigns affect the other campaigns the Japanese were launching in early 1942, or this the "tight schedule" over exaggerated?
The initial Japanese offensives (Luzon, Philippines, Borneo, Malaysia, etc.) was so resource limited that even if every transport and landing force they used had been assembled into a single force, you're talking 12-14 brigade group/regimental combat team equivalents (in British or US terminology), so, realistically, maybe four reinforced infantry divisions and some corps and army troops - that's it.
And that's for the most important Japanese offensive of the conflict, and one they have - literally - months to years (?) to plan, refit, and train for...
Now, that's pretty impressive for 1941 - the Allies didn't mount anything comparable until TORCH in November, 1942 - but still; in terms of priorities, that was the Japanese equivalent of, say, OVERLORD, in terms of amphibious operations designed (ultimately) to win the war.
Also worth noting is that after the initial series of offensives in December, 1941, the Japanese never had that many divisions afloat and combat loaded simultaneously again for the entire war...
The US and UK were mounting equivalently-sized operations from 1942 and they only continued, and got larger in scale, to 1945...
Best,