Qualms?If you were to identify for any of us what in this Wikipedia research you have qualms about it might be easier to discuss this matter:
Japanese language - Wikipedia
en.wikipedia.org
I know the Japanese borrowed Kanji from the Chinese, but did they borrow the words from Chinese as well?
Why did the Chinese let them borrow?Yes, they borrowed words, as well. Many of them.
The same reason banks lend money - interest.Why did the Chinese let them borrow?
Paid back as some sort of tribute money? I assume that occurred some hundred years ago?The same reason banks lend money - interest.
The Japanese paid back all the words they borrowed plus many new ones like kamikaze, sushi, geisha as an interest.
Don't underestimate foresight of the Chinese.