I wouldn't waste time explaining to people that it will take them a long time to become fluent in all aspects of the language. Anyone with half a brain knows that's true of any language - anyone who thinks otherwise is either in denial or thinks very highly of their own capacity. Either way, that explanation is simply a waste of time unless you have a personal goal of scaring the less serious students out of your class.
The way I'd -like- to structure a Japanese class is to have an introductory lesson, tell them about the importance of Kanji, and then have them go do RTK and come back in three months to start learning the language to go with the characters, but that's not realistic.
Once they are there in the classroom, I'd go with a light-on-kanji or even no-kanji approach (hiragana and katakana from the start, though. They can have a week of romaji crutches before it's all kana, I suppose.)
I'd focus on grammar explanations and start with plain forms, because that's the direction the grammar logically builds in and gets people soonest able to get from written words to dictionary entries for any independent study/reading they do. (But for various reasons, like not getting lynched by a mob frightened of the monstrous army of plain-speaking barbarians I'm creating, ahem, I'd get to basic formal with masu/desu conjugations within 60 days, closer to 30 if possible.)
Ideally I'd want to give them a fair amount of text and matching audio to work with, staying in the 1500 most common words as much as possible (that's the 1500 most common words from a mixed corpus of fiction, scripts, textbooks and magazine articles or some such representative set - not the 1500 most common words from the leading financial newspaper, ahem.)
Partly I say that because the first few hundred of the most common words are almost undefinable, intrinsically part of the grammar (hello いる、 しまう、 and 気) - those words are ideally taught with a teacher to ask questions of, unlike the average noun or verb that has only one meaning or at worst a few closely related meanings. Partly I say it because I would have such a class be quite limited in vocabulary - face-to-face class time is all about building grammar. Memorizing is a fundamentally solitary activity anyway.
And partly I'm trying to say I want a set of example dialogues that are very much what is called 'comprehensible input'; use the same words (and common ones) over again in different ways to reinforce the vocabulary and demonstrate the range of the grammar.
Oh, and of course, my dialogues would be fresh and interesting, and flawlessly performed. There'd probably be a major cinematic film based on them, they'd be so exciting!
Well, okay, you can only do so much with the other restrictions around example dialogues, but for goodness sake, I'd teach 'dropped' 'lost' 'stole' and 'police box' in the same lesson where something important is stolen from the characters instead of asking directions at a police box in one chapter, dropping a pencil in another chapter, and using 'lost' and 'stole' only to chastise a child character.
(You did say we had the funds to -create- the course from scratch right?

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