Hey, I'm also in the Orlando area -- I definitely recognize the locations of #2 and #4 ^^
Guess I'll put in my two cents:
1. Having the sunlight in the behind your subject is "risky" in the sense that it could either help or hurt your photo. It isn't something I would normally do unless I had good reason to. I do like the the lens flare, but it seems that your camera sensor couldn't handle all of that light coming in (could explain the red banding). The back-lighting also caused your subject to appear really dark, which can be fixed with a well-diffused fill flash. Other than that, good pose and good angle, but do watch for cropping of the hands and feet.
2. MegaCon 2012 - OCCC South Concourse lol... Yeah, I pretty much agree with Bruce on the lighting on her face and the eyes. It's something I would much rather catch during the photoshoot and attempt to "fix" it then, rather than toying around in Photoshop. As for the wristband, it wasn't noticible enough for me, but you could always try editing it out and see if you like the results. Good photo, though, and good light balance.
3. The pool fence is distracting, and the cosplayer is backlit here. I think both issues could have been solved by swapping positions, or entering the pool area, even.
4. One of the reasons I don't like the Wyndham Resort is that its one hallway is so crowded. If at all possible, try scouting out a location outside nearby the entrances to avoid the crowds. Nine times out of ten, the cosplayer is willing to go outside a for a couple of minutes depending on the heat. If you must get a hallway shot, try and find a lower angle to crop out most of the distractions and use a longer focal length from further away to try and blur them out a bit. Go easy on the vignetting here, because the overhead lighting is blown out, and you start getting a messy gray color in the lights if you vignette too much.
5. I'm going out on a whim here and saying this was at Holiday Matsuri 2011 (which I wasn't able to attend). But anyway, this is a cute pose. But remember to also pay attention to what's behind your subject. Just by rotating yourself more to the left, you would have gotten the stage out of the shot. The overhead lighting casted a shadow on her face because she was looking downward. This could be fixed with some fill light, or (since you mentioned you don't have an external flash) have her pose so that she's looking toward the light. Of course, this would require a completely different angle to make the shot, but it's just something to keep in mind.
You're doing great as a beginner ^^ Keep it up!
Convention Schedule for 2014
MegaCon・MomoCon・Knightrokon・Otakon・Anime Weekend Atlanta