Also remember to factor in some "thinking time" - as in, data analysis. You don't step right from collecting data into writing up the results, but you have to consider, organize, reorganize, write up and rewrite sections, etc.
Everyone forgets the thinking time (and sometimes, unfortunately, people get caught up in an endless cycle of thinking and not writing) - 2 years sounds reasonable to me (but then, I'm one of those too slow humanities folks).
Yup. Don't forget that qualitative studies, particularly ethnographic, can go sideways. Access to informants isn't possible or takes forever, or the data isn't there, or new questions pop up that you hadn't considered. Analysis can take a very long time. Transcribing interviews, if you're planning to do it yourself, is time-consuming (budget 4-6 hours per hour of interview). And then there's that element that no one seems to talk about when planning data gathering and writing in a rational fashion: life and the curves that it can throw at you.