Nice job! Hiragana are really easy, you can learn them in a few days! Katakana are harder because they are simpler so they're easier to mix up. The pronounciation is also pretty easy, but English native speakers shouldn't stick so much to their English intonation and stress, because it makes their speaking in Japanese rather funny to listen to. When is it common for Japanese to use numbers in kanji? In average texts?
Some comments, which could improve your flash if you want it to be informative for as many people as possible. You said the full "alphabet" of kanji is impossible to learn. But actually, it's not necessary. Maybe you should emphasize this, because when people hear about the large number of kanjis, they might panic and give up Japanese. I've found your explanation about the little つ a bit confusing. If I were a beginner, I wouldn't know the pronunciation of Gako-oh, but doubling the K is easier to understand - I guess. I think it's not a great idea to start learning with insults. Not only it is not a basic knowledge in Japanese, but it adds to the short overview that's supposed to be short.
Some presentation comments: At one point, the page order is like this: respect - honorifics - respect - honorifics. It might be a good idea to discuss one topic at once. Finally, I think it wouldn't be a bad idea to reduce the amount of text in the "Note" section. Bulletpoints and keywords are essential in presentation, because if people wanted to read a lot about this they would open a book, or search on Wikipedia, right? So presentations must be efficient: more information, less text.
Thanks for the review! >.< You really sound like a professional... O.O" I'm not the best teacher, and this was my first helping-tutorial-thing, so thanks for the great pointers!!! *I'll make sure to make a better one in the future that'll be more presentable, informative, and overall, more correct~