Too ambitious a goal?

Hi folk, First off, anyone here familiar with the Great South Bay Swim? Obviously, this year would be out even if the entries weren't closed, since my swimming distance lately is pretty modest. I swim about 3-4 days/week, but not far (1000-2000 yards or if feeling ambitious and have time, up to maybe 2200-2300). I've done one mile open water swims in bays and oceans, not fast (38ish mins. was fastest). This swim is 5.25 miles, so I suspect it would be a reach to be able to swim this next year... but out of the question? Or would it be better to plan for two years? I also run regularly--about five days/week, including two interval workouts, long run of abt. 2.5 hrs--so I'm generally fit, if not speedy. So, first question: do you recommend making this a two years from now goal or do you think next year is doable? Second, can you suggest some good training plans? Note: although I'm currently swimming on my own, I expect to return to the masters' group I swam with during the winter/spring. (They change their location/time in the summer...doesn't fit my schedule). As for type of workout, I'm more or less winging it, depending on how much time I have to swim on any given day. The USMS site has yielded some helpful workouts, and my coach also e-mailed me a bunch of practices of different distances, but I suspect I'll need a more organized month-by-month plan to get from here to a 5.25 mile swim next year or the year after.