Designing of the system up front will save on costs, setup time and complexity. Many a project has been thrown together and it ends up being more complex, taking more time and costing more. This first 3-5 percent effort in a project will define the rest of the cycle, so take time to really figure out what you need.
It is best to take a picture of your house and draw out the lights that you want to decorate the house. And realize that this is a long term plan, where a few lights strings can be added each year until you reach your final design.
Wiring and power will be a significant portion of the costs for lighting. It is important to plan the layout of the lights to minimize these costs. The bests layouts are modular in design, where each element is easy to add or move in the display. In addition, it reduces costs to group the display elements, so a common controller can be used for multiple elements.
In the picture above the power is omitted, but there should be one extension cord run to each group of lighting elements. Then with in each group, there will be shorts wire runs for power and control. I have driven past displays where there are 15-20 extension cords running from the front of the house out to the front of the yard. At 18 cents a foot for 18/2 lamp wire, this is easy over a $100 just in wiring. With that amount of money a local controller could have been used with one extension cord to the group. So realize that saving in one area may cost you more in another. The end goal should be to spent most of your funds on the actual lights.