You should probably leave France alone and let it recover or collapse. That way you can get back to the far more interesting struggle with Austria. I think you should try to strengthen France or, better yet, try to get Burgundy to conquer and form France if you can. That will ensure a strong France going forward and that way, if and when you defeat Austria and crush them, you will have a strong France and strong Russia on your borders. If you decide to leave Austria alone, which seems like the way that you might be going, then conquer as much as France as possible for yourself and Burgundy. I do think that you should take at least Austria's northern territories though that border you.