with dedication, you have enough time to train. It does sound like your long distance cycling experience may be a little lacking, hard to tell from here. If I were doing it, I definitely would want to ride a series. You don't say where you are or how far you would have to travel to do that, most of us do have to travel some to complete a series.
I am not sure what to say about eating. I have adopted a liquid diet, but that might not help you if the water is of questionable quality
I have never done a 1200k without being in pretty good condition, at least for me. Flat can mean winds, so there is that to consider.