I am 5'11", weigh 185 lbs, and wear a size 16/18. I will still be cosplaying Mello at the next con I go to assuming I get my shit together and finish the costume.

DO IT. People who mock cosplayers for doing what they love are the scum of the Internet and their opinions should have no bearing on what you do. If you have fun and return with good memories, you've done more than they ever will.