Vitamins/minerals can be taken with thyroid replacement medications; however they should be taken with at least a 4 hour separation from thyroid medication, as they can inhibit absorption of the thyroid med. .
Yes. You can take multi-vitamins. Armour thyroid has been around a long time and many physicians consider it superior to synthroid. As to "what brand of vitamin is best" that is a "how many angels are on the head of a pin" question. Purchasing vitamins in a store specializing in supplements, rather than an ordinary drugstore, will give you a better product selection.