I'd like some advice on Japanese grammar...

[41-Inches-Wide]

Well actually, you use hiragana when you write japanese words in japanese characters. you use the katakana for words borrowed from English. Like "AISU KURIMU", it is written EXCLUSIVELY in katakana.
There is a big difference between hiragana and katakana (curved vs. angled strokes), to stop it from being all wierd and messy. It's like this, if you write AISU KURIMU in hiragana form, the japanese will be all like WTF MAN, DUN UNDERSTAND. But when you indicate through katakana that this is a 'borrowed' word, then it's all good.

As for the kanji, that's a pretty long story i dont understand it myself I am terrible at kanji. But anyway you only use kanji for the specific japanese words that have their own characters. Like for example, you don't write FLOWER in katakana (FURAWA-.xD) because it has a japanese equivalent already, which is "HANA". But they use kanji to signify -AGAIN- the difference of the various 'hana's' (i.e. hana means nose) also. The HANA "nose" has its own kanji. And the HANA "flower/blossom" has its own also.

EDIT:
Long-ass post. hope i helped a little