As promised, here is a summary of the responses I received to my query for information on Japanese kanji, kana, and word frequency.
All frequencies are, ideally, counts from a corpus of informal written correspondence.
Frequency of individual kanji characters. Frequency of words. I counted a total of 8,400 characters from each group. I counted Kanji, hiragana, katakana, romaji, and various symbols. Hayashisan sent a file with kanji frequency counts.