New Worlds, Old Worlds, and Things In Between

As a primarily fantasy author, it should go without saying that I love world-building. In case it needs to be stated, well, I just did. Right now, I'm working out a story that's not quite fantasy/sci-fi, but neither is it historical. Can you guess? It's steampunk. (Natch.) I'm finding the creation of an historical-yet-fantastical world particularly challenging. How much do you stick to reality vs. how much do you fabricate? How plausible does your "science" have to be? How detailed do you have to get? Is it better if you just stick to general, broad descriptions of the tech? How historically accurate do you need to be, or should you veer away from historical events completely? I've read a fair amount of steampunk at this point by a variety of authors, and each finds his or her own balance, some with more success than others. I'm convinced that a solid knowledge of events of the time is the cornerstone of good steampunk. After all, when you know the rules, you can then choose how and when to break them. Of course, that means I wish I remembered more of my local and national history classes. Time to hit the books!