I am trying to answer your question, eve.]
Regarding sentence structure. According to Ken Buttler, an American professsor who were awarded medal for creating speedy curriculum for foreign learners here.
Understand a Japanese "sentence" "Japanese CyberTutorial 3 Japanese has no real SENTENCE
[edited:grammar]. And every word is separated by a function particle, the so-called てにをは in japanese.
You use this function particle to make words meaningful, so if you want to speak japanese well. Forget your english grammar for a second and try conquering this function particle. You can buy a book called Dictionary of Japanese Particle, I got one of this myself, which is probably very useful for all who wants to learn real Japanese.
On multiple scripts:
Japanese maintain multiple scripts as part of history progress, and perhaps government language policy and also the culture of Japanese mindset to be all embracing. There is no point trying to unify the scripts into romaji or just hiragana, it will not make sense for Japanese. Japanese use multiple scripts as signal just like an XML tag on each word. Simple example for this is Japanese love to use カタカナ for words usually written in ひらがな in magazine as attention marker. For Japanese that is like putting BIG CAPS or double quote on a word. Japanese choose their words carefully in writing. A balance use of 漢字、 ひらがな and カタカタ is what makes a good sentence.
Of course this might to be ideal for language learners of others language, and might not be ideal of Japanese themselves, but they are deeply trapped in their language systems and just give time for them to evolve. But the way I see it, no matter, how Japanese evolves in the future, a single script will never arrive, given the culture of its people.
ax