Enchanting Questions

I got a couple questions on enchanting, but feel free to put your own questions down below.

1. Can you stack some enchantment effects? For example, the Advantage enchantment. Can you wear multiple instances of that enchantment to increase a single skill? If so, which can and can't you stack?

2. Are Spell Matrix enchantments one shot things? Or can you enchant it so that the spell can be used multiple times?

3. Does the armor enchantment stack with other armor enchantments or spells that provide armor?