Wonder if it would be broken if it scaled 5 ac per spell slot.

Yes, that would be incredibly broken. 

My fighter has an AC of 19... if I take the feat magic initiate (cleric) I could buff myself to 21.. and I'm at level 4.

What is the rang? 

Does this move with the creature you've cast it on?

What happens when you cast this at higher levels?

Why doesn't it have a buff when casted at higher levels?

Quote from Sandmugger >>

Why doesn't it have a buff when casted at higher levels?

 Because that would be quite broken.

Quote from Grrurk >>

Does this move with the creature you've cast it on?

 Yes, it is not a dome or magical projection, it is just a temporary enchantment on their body / equipment.

Could this spell be used by a cleric to make a magic shield +2?

I personally do not see why not following logical rules with your DM.

If you somehow have access to the twin spell metamagic you can.

heavy armor plate and shield  AC 20    +1 Blessing of the forge, +2 for shield guardian, +2 for shield of faith , +5 spell shield...... = AC 30

If the target of this spell is ever more than 60 ft away from the caster before the duration of the spell is up, does the spell end?  Is there an official rule for this or is it DM discretion?

They would only need to be 60ft of the caster when it is cast. Then, the spell is like an enchantment in effect. They have +2 AC as long as the caster has concentration.

Can a cleric of the life domain use this skill even though it's in the war domain?

Quote from FerrariaExpress >>

Can a cleric of the life domain use this skill even though it's in the war domain?

 It's still a cleric spell, so any cleric may prepare and cast Shield of Faith. The listing of War Domain simply references the fact that War Domain Clerics will always have SoF prepared as part of their War Domain Spells class feature, similar to how Life Domain always has bless and cure wounds prepared as part of the Life Domain spells class feature. Any subclass that has a spell always prepared or adds a spell to a class' spell list in a short table like those Cleric subclasses is listed on that spell's page.

I believe it is cast on the creature not equipment.

I was writing a paper about this I thought  it was 20 ft not 60 ft lol :|

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i love it ;3