If you use vanilla extract, be sure to get one which is alcohol based. If you used one with glycol base, you wouldn't be able to use enough to have the impact you want. You don't want any more than 5% glycol by weight. You can use as much alcohol based vanilla as you want because it evaporates permanently. My experience is that rum doesn't really come through, even in large amounts. I've never tried rum extract. In pipe tobacco, a vanilla extract to tobacco ratio of 1:2 (by weight) is my preference. That's a good, noticeable but not overpowering amount.