N/W Shield or Energy thing?

I am debating as what to use and need help in knowing if I should use shield or hold one of those items that give extra energy.

It really depends on what you do most. Most Necromancers tend to cast more than entering into melee, but you might be a melee Necromancer, which entirely viable. If you find that you run out of energy, go for a Focus or an Idol. If you find that you need more defense, get a shield.

Or, better yet, set up two weapon sets!

You can do both. Weapons sets will allow you to set up as Necro and Warrior with the push of an F key.