I had both nipples done, but let them close up - long story, but no problem with the piercings.
Then about four years ago I decided to get my left one done again and it's still in place.
I wouldn't say they were supersensitive all the time, after you get used to the feeling of it being in there, but your nippple will be erect more or less permanently if the piercer places the bar correctly.
If you have never had any piercing done before, pay attention to the after care instructions, it will save you a lot of grief in the long run.
It will hurt when the needle goes through and ache for a day or so afterwards, but hey, you're a big guy I'm sure you'll be fine.
Good luck with it and enjoy your new body image.
PS A PA hurts a hell of a lot less and heals twice as fast...