I've done a fair bit of con-hopping and cosplaying [http://i1176.photobucket.com/albums/x326/SageRuffin/Magfest%208/Sage-K.jpg] to boot [http://i1176.photobucket.com/albums/x326/SageRuffin/Katsucon%2017/SageWinduwithSaber-1.jpg]. I might be able to help you out...
Angelus SnV said:
1) Different hairstyles than th'one the character usually depicts
I'm one of those guys that's kinda anal about accuracy,
BUT if the character does have an alternate hairstyle at some point, it's fair game.
2) The obvious gender swap
One of three things are gonna happen:
1.) no one will care
2.) it will be met with disdain or flat out disgust (usually for male versions of females, i.e. Male Cammy from Otakon [http://i1176.photobucket.com/albums/x326/SageRuffin/Otakon%202011/DSCN1587.jpg])
3.) it will be seen as "cute", "sexy" or whatever other variation thereof. (usually for female versions of male characters, like these two rolling as Yuri Lowell and Capt. Karol Capel [http://i1176.photobucket.com/albums/x326/SageRuffin/Katsucon%2017/DSCN1534.jpg] from Tales of Vesperia)
3) different race of th'cosplayer than th'character depicted
This is tricky one, as I've had my share of this particular blunder in the past. Long and short, sometimes [http://i1176.photobucket.com/albums/x326/SageRuffin/Katsucon%2015/RSCN0819.jpg] it [http://i1176.photobucket.com/albums/x326/SageRuffin/Otakon%202009/DSCN1011.jpg] works [http://i1176.photobucket.com/albums/x326/SageRuffin/Katsucon%2017/DSCN1549.jpg]. Other times [http://i1176.photobucket.com/albums/x326/SageRuffin/Katsucon%2016/DSCN1226.jpg]... well, you get the idea.
Fighting games tend to be pretty forgiving, but it usually comes as part of an alternate color scheme, and that scheme is usually engineered so that the outfit still matches the character. It usually a good idea to go in a color scheme
OTHER than the default, but many people don't realize this.
4) Overweight/Underweight cosplayers
What do you mean exactly? If you're talking "overweight" in terms of body mass index, I don't think anyone's gonna care too much [http://i1176.photobucket.com/albums/x326/SageRuffin/Otakon%202009/DSCN0876.jpg]. If you're talking "heavy-set [http://i1176.photobucket.com/albums/x326/SageRuffin/Otakon%202011/DSCN1702.jpg]", then I don't recommend going as a super-hero unless the hero in question was kinda heavy-set him/herself, at least not without running a few laps around the block first. If they have an alternate outfit that makes certain parts of the body less visible (if you get me), then I advise going for that.
Of course, this is dependent on how self-conscious you are of yourself. If you don't give a shit, then by all means, dress up and enjoy yourself.
Hope this helps. Whatever happens, have fun. ^__^