Hi - Is there anyway that you can post a picture of your quilt? That would certainly help with giving you some ideas for how to quilt it.
As for the batting, I usually cut my batting 3-4 inches larger than my top and then the backing about 3-4 inches larger than the batting. I quilt on a regular sewing machine, i.e., not a longarm so I don't need as much overage. You should have some though, because the quilting will take up the fabric and you'll need the extra to square the quilt when you're done.