Herbs: Amount and Potency

Does the amount of herb taken affect the potency? Example:If I'm taking one capsule for its anitbacterial properties, will it be stronger and work better if I take two capsules?

Yes, more of the herb will mean a stronger dose, but no, it will not necessarily work better. Often with herbs, an excess dose will cause side effects, or will produce the opposite of the desired effect.
The dosage of herbs is not an exact science: herbs vary in potency according to the soil they are grown in, when during their growing cycle they are harvested, and how they are processed after harvesting. Because of this, it is important that you choose good brands of herbs. Often, the smaller companies take better care of harvesting at the best times for potency and preparing herbs without a great loss of potency. Try to do some research for herb companies in your area.