.2 Belt and Bulge on every ship like normal. I wouldnt start AW until KGV, POW, or L1. But if you are playing blitz, you can always adjust that according to how large of guns are being fired at you. I put 12inches of belt on New Orleans in Blitz. Tough to sink I was.

Q class and Dido/Sirus are about it untill you get to bbs. You can put armor on anything of course but in most cases it wont be enough to help.

The  L class DD and County class CA can be AW to some degree the L class belt only and county can go either or I managed to get 15-21" of belt at time with random set ups just screwing around.

If you're looking to do it just for fun, use the lvl 28 4" triples D on L Class, with skeleton crew (just the BO and gunner with minimal recruits on them) and the front guns, and use all the weight left on belt armor. You'll have over 10" belt and one fo the most fun troll ships in the game. If you're looking for something a little (just a little) more serious, Q Class with skeleton crew and 4 6" singles and belt is an awesome ship to train your manual aiming skills.

Well Emerals is also capable of being AW (belt) but it restricts possible gun setups to weak and short ranged 4' trips or something.

Nice for a blitz DD brawl in the middle but not as good for everything else. 

Well, that's the point of 2 frontal 4" trips L Class :P You just rush into the enemy and beat him down with your reload speed. 11" belt does wonders against torps too.

Spam belt on your PCL.