Iteration: Rome was not build in a day. So is your product. Your product is not going to be build in one shot. So dont waste too much time thinking about the minutest detail in the very first iteration. Spend your time, identifying aspects that you are sure off and then implement only that. The act of implementing something that you are sure off will help you understand other related things that you are 100% sure off.
More the iteration and shorter the iteration cycle time the better.