I'm in the same boat. Came back after 18 years off. I needed to lose a lot of pounds, I've lost about half; based on your diet question, you're probably in that boat too. I'm in Madison, WI, so my winter is plenty white. Here are my thougths.
(1) Keep it fun. Trying to bike in the winter is a great way to stay in cycling shape. It's more likely to be fun if you can get the right equipment together. If it's fun, do it. If not, do something else (see below). Same thing goes with training in general. When you quit having fun it is harder to keep going.
(2) Cross train. Swimming helped my neck and back problems. Ab/lower back work is also helping. Recurring injury (inner thigh, related to tight IT band) is being addressed by specific exercises (professional PT). Skating would also help outer an inner thighs. Point is, there are lots of things you can do off the bike to make riding the bike easier on your body and to help you avoid injury. You don't have to become an athlete. I don't do everything every week. You can just get on the bike and go to Cali tomorrow. But sooner or later you're going to have to do the work, so you might as well get started.
(3) Listen, don't diet, when on a multi-day tour. Dieting plans are great when you're training, and essential when you're not training. On the road, on a 3+ day tour of 50+ miles per day, it can make you miserable. I lost more weight and was happier by listening to my body and finding the right mix of foods than by counting calories or points. For me, oatmeal and fruit at breakfast. Mix of fruit and complex carbs for snacks. Low protein and limit the dairy while on the bike. More protein off the bike. I lost over 10 pounds on a 7 day tour this way, while just listening to what my body said about quantity needed. Your needs will probably vary. But save the diet plans for the rest of the year (and especially for the week after you get off the bike).
(4) Goals are great, fun is better. Goals keep you motivated, and let you see your progress. If I were in your boat I'd make monthly goals up to the departure date. But recognize that life, weather and your body will get in the way. I've made about 2/3 of my goals. I'm sure I could have done all of them, but there were times when NOT making the goal has kept me riding. Be smart.
P.S. Tandem - You wrote, "Personally, I have found Bill Phillip's plan ( http://www.ediets.com/diet/bill/
) to be very effective for me. When I started with it I was overweight and constantly feeling like I was dragging. I've been on his plan for about 4-5 years now and it has only cost me 40 pounds and a feeling of having enough energy to make it through the day and then some." I can't figure out how to see the plan itself.