Resistance to Cold, Fire, Lightning, Poison, etc

[AreaOfEffect]

Resistance bonuses all stack. So a fire brand and elemental fortitude (that nature spell you couldn't remember) will grant 100% fire resist.

You can go over 100% fire resist, but it won't have any real affect. Yet you might want to keep that in mind if you want to cast a spell like stoneskin or ironskin which grants a resistance penalty.

The bonuses from any two of the same item will never stack. There are very limited cases where equipping the same item twice has any benefit. Mostly just equipping weapons and shields for their extra attacks or increased parry bonus. There is a rare case where equipping two bracers while under the effect of a full earth bless or legions of steel will grant more of armor, but only from the enchantments.