I don't believe this distinctions between wago and kango is going to
help you with counters.
Often you may have a choice how to count things. For example, you can say
You can also say
which does use the counter 個 used for small objects like apples,
eggs, bars of soap, etc. However, not everything can be treated like this.
By the way, 年 is used for counting years, even in duration, in minna no nihongo. I notice 年間 is more common. Is there any subtle difference?
Both 年 and 年間 are used for durations in Japanese.
I don't know which is more common, but 年間 is more formal or correct here.