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
りんごをふたつください。
You can also say
りんごをに個{こ}ください。
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.
Counters, in a manner of
speaking, clarify what you're talking about. Just
consider in English the difference between saying "two
sheets of paper", "two reams of paper", and "two papers".
All three make sense, but express very different ideas
(particularly the third).
On many points of grammar, Japanese is very
regular--particularly when compared to Indo-European
languages. However, when it comes to counting, there are
numerous exceptions.
I think a good principle to keep in mind is that the
numbers one, two, and four frequently enough have
their own idiosyncratic forms of expression. And, it is
this that is perhaps leading to some confusion for you.
For example, when counting people, the following are the
standard:
一人{ひとり}、二人{ふたり}、三人{さんにん}、四人{よにん}、五人{ごにん}
But if you were counting large objects like cars, you would
use
一台{いちだい}、二台{にだい}、三台{さんだい}、四台{よんだい}、五台{ごだい}
I would recommend that you learn the following
- how to say the names of months
- how to express the ages of people up through 20 years old
- how to count people
- how to express hours and minutes for telling time
If you say something like 彼女はにじゅうさいです, you'll
still be understood and most likely someone will point out
that the Japanese say はたち.
Years ago when I was living in Japan, late at nightreturning home from work, I might stop off at
a yatai for some ramen and yakitori. Whenever I ordered や
きとりをにほんください, I always got teased. For example,
someone might chime in saying I was a cannibal; someone once
made a comment about whether I intended to eat my
chopsticks. I have no idea whether they were just punning
me, pulling my leg or whatever (I learned a lot of
interesting Japanese eating at yatai). But, if I said, やき
とりをふたつください, no one blinked or made a comment.
