Going to depend entirely on how seperate they really can be, and if you can deal with that, and the tenants you get. Get a few college kids in there that party all the time and it will suck. Get a couple nerds in there that play video games all day, then it might be alright. haha!
Also, don't base your rent on your mortgage. That's dumb. If the going rate for 3 bed, 1 bath is $1000 a month, then charge that. Don't give a discount just because it's not costing you that much.