Hi Matt,
I don't think that any of us working with any sort of artistic endeavour are a stranger to what you describe here.
To be held back by the mere thought of all the possibilities "out there" - all the different sounds, themes and styles ect.... what to do? how to start? where to begin? and so on and so on...
It's not the easiest of thing in the world wanting to create something lasting and "worthwhile"...
But a good place to start is getting your ideas down on paper - not only the thematical/stylistical ideas - but your general ideas of what it is you want to do. Writing them down often helps (it helps me in any case) in getting a better overview, and while it still might seem like a neverending task is still in front of you, I feel it helps me be more concentrated on the individual thoughts - instead of only having them fly around in my head.
Being creative and getting something worthwhile from your endeavours in music composition is about 10% inspiration and 90% perspiration (as is so often said) - 10% of the work is the "Godgiven talent" the "devine inspiration" ect... all the other is plain hard work (still to do with some talent of course) - but it emphasizes more on what you know about music and what you can/want to do with different sounds/instruments/programs ect. ect. than getting an original idea.
Music making is in some ways an exploration of the (musical)universe - sometimes going places you've never been (and might never return to) and sometimes it's exploring allready know material in depth.
The easiest thing is giving up - try making it the most difficult thing by emerging yourself in the world of sound and play with your ideas - sometime you might end up with spending a lot of time on things that don't work - but still, by doing so, you are continously learning what to do and what not to do. The only one to judge whether something is worthwhile, in the end, is you.
Don't be affraid of using too much time on stuff that might seem simplistical - sometimes it's actually the most simple things in life that works best.
Get your ideas out of your head and on to paper or something else from which you can reflect on - discard and reedit. - Sometimes overview is all it takes - sometimes you might need to go read about something or listen to recordings of how things have been done in order to express your thoughts the way you want. Originallity is not always "what to do", but often "what not to do" and with a greater knowledge of the "world" in which you're living and the possibilities the options grow. But just don't get caught in the "the more you know the more you discover you don't know" and keep on writing down and processing the ideas you have - there'll always seem to be ways to do things better - but it's the way you can do things with your current abillities that counts here and now!
Good luck!
Thomas