Honestly, I don't bother. I use the level 30 3.46"/76 SK C/32 AA gun on the main armaments with either nothing or torpedos in the 2 sides. The only time that something will really get that close for you to damage it, you'll make better use with a torpedo spread than trying to switch guns and kill it.

I generally assist a battlegroup in north or south and keep to their rear so you'll be safe from BB salvos and at the correct range for striking planes that fly over. Sometimes you'll have to switch battlegroups depending on who needs the most help and you might run into a DD or an SS so you can deal with that if you wish. Another option is to get a sonarman to act as a spotter for your team. I suggest not to bother too much with other roles in the fleet as you are far too small to do any damage in a GB. The longer you stay alive and shoot down planes, the longer the bigger ships can advance and keep the smaller ships off of you.

Don't put AA into your T slots because they will work against your main armaments since you'll be fiddling around with angles. The best for the Emden is the level 30 3.46"/76 SK C/32 AA gun (You can find more information here). How it fires very quickly is to keep setting your Firing setting to Gradual (F4), start firing and then immediately switch to Maximum (F4) and you'll be firing full salvos at twice the speed; thus you'll never need any other AA gun.

Hope this helps

We're only talking about AA escorts.

I run an Emden with a 2 L45 AA gunners and 1 Sonarman.  I mount them on the R slots and put the L32 3.46" guns on.  Any FCS works, but I run an SS III version. 

I also load up a UK Emerald with two L61 AA gunners and 1 Sonarman.  I run the L45 machine gun versions in the R slots.  Same FCS.

You cannot run HE and AA ammo on escorts at the same time.  AA only or HE only.

You can have different gun types (small singles on T and twins on R), but they have to be the same front and rear and same ammo type.

I didn't claim to be talking about anything but AA escort. I also use the Emden as I'm a KM only player at this point and suggested the l30 3.46" AA.

Also to answer the last part of the original post, the addition of a T slot doesn't really add to the firepower that you have already. Armor won't do anything except slow it down. You're bringing a CL with aproximately 8000 into a game with BBs, CAs and SSs that can tear you apart with one good salvo. Armor isn't really necessary at that point and speed will be the most important factor. You want to be able to not only move between battlegroups in persuit of planes, but also escape while under fire.