Agreed, better to be safe than sorry.
We go off of the International Costumer's Guild level guidelines. Here they be:
http://www.costume.org/documents/fairness-26-05-2006.html Scroll down to "Skill Division Guidelines"...they call them by different names, Novice = Beginner, Journeyman = Intermediate...Master is the same. You can't go wrong entering on the higher level. However, if you would like to enter under beginner's, the main thing to ask is, have you won anything in a costume contest before? If Yes, go intermediate to be safe. Regardless, as the rules say:
"Contestants may sign up for the category they think they belong in. However, the masquerade area head and the craftsmanship judges reserve the right to move contestants into a different category based on the work presented."
So, I wouldn't sweat it too much. It's mostly to be sure we don't have vastly experienced individuals competing in beginners just to pick up some prizes. It sounds like you don't have anything to worry about either way. My advice based on my own personal preferences, stretch your limits. If you feel your skills are that of an intermediate cosplayer, go intermediate, regardless of how many costumes you've made. It's skills and wins that really determine where you should enter.
...no. No fire. No water, no glitter, confetti, small rabid rodents, anything like that, no matter how accurate to the character it may be. Sorry. ;p
Go ahead and crawl or limp or anything when you get onstage, but I'd say move up the ramp toward the stage at a pretty good clip. I'm not saying run, but if you're going to crawl, don't crawl up the ramp, you'll use up your whole 45sec just on that, and presentation judging doesn't technically start until you hit the stage. Dancing would probably be fine up the ramp, though. Once you're onstage, you can dance, crawl, hop, skip, whatever. Thank you for doing so, it's much better for your presentation score to put lots of thought and effort into those 45 seconds onstage, rather than just waving and running off.
The rules state: "NDK’s masquerade is rated TVPG (Parental Guidance Suggested)". That's a good guideline for your music selection. If you have any worries, I'd run your music choice by Katie, the head of Cosplay at NDK.
If you have any other questions, feel free to ask.

Here are last year's contest rules, although they change slightly every year to adapt things like "no throwing weapons" or "no cracking whips at the judges". Little things like that. ;p
http://ndkdenver.org/activities/cosplay/contest-rules