i personally try not to rely on templates but im not as well versed in web shit as fdigl so sometimes i get lazy but let me tell you working on your finished product that you built from scratch maintaining it and improving will be over all easier cause you know what you're looking at and where you need to go. With editing templates a lot of people leave loose ends just by wiping half the page and replacing some text. So from the bottom up is definitely the way unless you're just trying to get a fairly functional website that has a basic task and you really don't care about looking like 100000 other people using the same template. When you click on a website you can often tell who used templates and who didn't. Good luck creating!