It's all part of the design process. I've two unfinished projects at the moment that I still need parts for and then the time to work on them. On top of that i always have different ideas for possible future builds. But once you start you have to make decisions as you go but till then there is always choice.
And yes I do buy stuff from E Bay, but only specific parts that I know what I want in advance, just the same as buying online from other sources really.