Kamala-
It sounds like you have the right attitude to make this happen. That is half the battle. I am not a big as you, but not by much. I will be doing the Livestrong ride as well, but only the 70 miles with my wife and her boss who thinks the 70 miles is only a training ride! I have not really ridden in 4 years, but I am motivated to get into shape so I can ride this. I rode once before Christmas for 20 miles. It took almost 2 hours and I can not tell you how exhausted I was. It was really hard. I have ridden several 100Ks before and I was more tired on this 20 miles than I ever was on the other rides. I can not wait to get into shape to do this.
I hope that I see you there.
Ron