Thanks for the extensive feedback. I'm happy to find a japanese student here!
I have to say i'm a basic student,and some of my game design choices might oversimplify or accidentally misrepresent japanese
That being said, let me focus on specifics.
You're right, 本 means book, and that's how it's used most of the times, but it can also mean origin when compounded with other kanjis, and it has multiple forms: 元 基 素. So for example: 本当 means truth, 本 here means true/origin and 当 right/apropriate. Or, 基本 means basics/fundamentals, here 基 means fundation/origin and 本 reinforces the idea of origin. In the end, since I wanted to compound the word Nihon/Nippon/日本, I had to present 本 as origin, as in "the sun's origin". The link you sent explains very well how 本 got its book meaning, but it doesn't mean 本 lost the "origin" meaning
Indeed, Nichi 日 has many pronunciations, but I took a gamedesign decision here to limit the correct to one: "hi", since it's close to "Ni" in "Nihon". Adding "ka" as an option was a bad idea, thanks for reporting it. About its meaning, just like 本, its usual meaning, when not compounded, is another one: (day), but I had to present its "sun" meaning, so I could compound it in 日本. We usually use 太陽/たいよう for sun as a vocab
女 usually means female, and compounds in multiple vocabulary related to woman. I decided to go for 女 = woman because it's more digestible for english speakers (imo)
月/げつ/getsu means month, but I didn't have enough space to expand on that, and I wanted to use the mnemonic moon+sun = bright(明るい/akarui or 明/mei when compounded )
to get both 休む and 明るい you have to combine 人+木 日+月
Thanks for the "shi" idea. That's a really good piece of culture.
物 is also a great idea,thanks. It compounds in a lot of useful words
I was planning to use repetitive radicals as in 木, 林, 森 and 森林 as the third wild card: exploration of the beaten path. But I didn't have enough time i.i