You want to fully write that book? You don't want to stop half way? Then be realistic with the approach. Be realistic with the concept of your story- to the setting, to the plot, to the characters of your story. Starting from your concept (the ideas behind your story)to every other elements that make up your story, you need to be realistic. Sometimes certain idea pomp into our head, we love them and we want to work on them but we do not look at the dept, to see how realistic they are. The concept might be beautiful as it dropped to your mind and building something meaningful on it might just not be possible because as you go on it might get water down or too complex.
When a story idea come to your mind, be calm. Test it. Test your idea- within your mind try to build up your story and see if it will end meaningfully with good purpose . It is not all about the beautiful start but also quality body and good ending. If you are able to think your way through, with believable story that had a good ending then you can go ahead.
If it is not realistic, then it will collapse on the way. Though you might be happy starting it, how about developing it. Make your setting realistic, if you try to bring setting not realistic you might eventually get stucked and not be able to proceed. So also the sequence of event, that have to be realistic and achievable, something that humans mind can relate with or you might not be realistic.
There is room for creativity and innovation but must not be beyond the moulding of the mind. It must not be beyond the control of the pen. It must form a whole, not part. When you want to write a story, see it in it wholeness before you start so you don't get stucked or confuse and then drop the pen half