Japanese paint application wasn't very good, but it wasn't that bad. Japanese aluminum was actually pretty good. It was an alloy that was stronger than ours for a given weight, but it did corrode. The Japanese were aware that it corroded, but found it acceptable as it did not corrode in the intended lifespan of a given aircraft's design, e.g. by the time an A6M started to corrode there would no longer be any A6Ms in service. The corrosion took the form of whitish, metal flakes as I recall.
Your Ki-84 really does look like it spent about 20 years in the Philippine jungles.
As to the bullet holes, they are so tightly clustered the only way I can see them having happened would have been from something like a submachine gun while it was on the ground.