Braces behind the teeth SOUND like a great idea but yes, they affect your speech, yes, they hurt (braces will hurt no matter what) AND they will cut your tongue and leave it sore... and your orthodontist might not recommend it...
I personally cannot imagine the world of hurt I experienced on my cheeks and lips during my braces experience inflicted on my tongue. Afterall, when my teeth hurt so much I couldn't chew, my tongue was doing the "mashing" for me.
Talk to your orthodontist about it. I've seen a few fashion models, if that's the kind of agency you're talking about with braces so I wouldn't worry too much.

photo courtesy of lingualcare.com