The fabric will soften up some when the sizing is washed out of it but I would rethink using medium weight batting. Unless you live in a very cold climate that size batting will make a very heavy quilt.

For tying on this heavy a fabric I would recommend either using a very narrow grosgrain ribbon or using the heavier crochet thread (like used for bedspreads). If you choose to use yarn I would recommend using rug yarn which is heavier and I think is nylon instead of acrylic and thus probably likely to hold up better to the hard use it is likely to get.
For the tying I recommend using the really big fat sharp pointed yarn needle that comes in the multi-packs of 'craft' needles and you will find a pair of needle nosed pliers most helpful!

I sure hope you ladies don't mind, but I am back again for more advice. I sadly admit, I am a bit disappointed and frustrated. I have not came out and told my son that this is for him (wanting it to be a surprise) He picked the fabrics when he had asked before. This evening, I was feeling the waters about what he thought about the tying and explained the difficulty in getting the needle through to quilt and what have you. He asked who it was for, my response was "not sure". He asked for a boy or girl, my response, "boy" He says that the tie thing is too girly and that the thread should match the brown camo. (I have bought orange so that the quilting would stand out) I know this sounds plum awful of me, but I don't want to go through that amount of work if he is not going to like it. I went through that kind of total disappointment when I made a plastic canvas white tail deer head with a camo fabric background for his older brother. The frame alone was $85 because it had to be special made. After all of that, he didn't really care for it. I suppose I could go ahead and make it, find out his reaction without telling him it is for him.. then if he doesn't like it, I could sell it.

I use the twill camo from Joann's ALL THE TIME! It quilts just fine. My hubby has a nick name at work. "Camo Keith." LOL If I could figure out how to show a pic with this response, I would. I will try.

Instead of useing ribbon or whatever, just handsew your ties with regular thread. Really easy. All you have to do is sew a few straight stitches on top of each other, like sewing on a button, only without the button. then it will be tied and he won't think it's girly at all.