Distance Swim Progress Report & Questions

I hope no one minds, but I could use your input. And if I repeat myself, it is for the benefit of any new people to this forum. I am training for what I call an epic swim; a swim from the island of Roatan to Utila in August of 2008, the year I turn 60. The distance is about 19 miles. After months of not swimming by choice, I started re-training this past January 15th. Due to previous swimming injuries, I decided to not leap into it but to train smart so I don't have any downtime due to injury flareups. In January, I only swam Monday-Wed-Fridays and the yardage started small. My total from Jan 15 to the 31st was 8,800 yds. In February, I added a fourth swim day, Saturdays. I decided to make Mondays and Fridays drill and sprint days, and Wednesdays and Saturdays are distance days, many times I time them to see progress. My total yardage from Feb 1 to Feb 24th is 26,980 yds. There were 6 days in there the ocean was angry and the swims were of short duration. Two weeks ago, I timed my 2nd 2 mile swim and it is down from a 54:07 to a 51:02 so I see progress, and not just in time but how trashed I felt hours after it. Last Wednesday, I timed a 1 mile swim and it was a 27:01 so that is rather slow compared to the 2 mile, but hey, we all have off days. Since that time, I have been extremely fatigued, I actually did not swim this past Saturday because I needed the rest. It is difficult doing a load of laundry. Now, I do not take vitamins because there aren't any here but I plan on getting a suitcase full when I go home to Texas in April. Also, it is hard to hydrate during training because the little island kids steal my gatorade and water off a chair on the beach. But I am not sure how important hydration is for a mile or 2 mile swim, but when I get into the 4 milers and I am about ready to break into those, I guess I'll have to figure a way like wear them around my neck or something. My questions are: do I need to incorporate periodization into my training routine (periodization is where you swim so many weeks on, and so many days off on a regular basis); what vitamins or replacement products would benefit me as I move upward into more mileage? The reason I am asking these questions is when I go home the end of April for a visit, I will be able to buy anything that may help my body regulate the training I am incurring. The only thing here is Gatorade and my problem with that is it may take so much of it, that my stomach will be sloshing around full of liquid; not a good thing. Sorry this is long, but wanted to layout the groundwork. So, periodization, pros and cons? Replacement products? Vitamins? Donna