3. FF,DD,CL only

I assume you are referring to the auto escorts that you setup to follow you around,
by way of the "Escort Setting" button, top RHS in the shipyard.

If so then...

1.- Use Aiming FCS

2.- AA escorts are the most popular (AA shells can't dmg other ships).
Auto escorts can only use the ammo in the A locker, they can't switch

3.- CL/PCL (tho PCL's cost alot more to repair)

4.- No

There is a basic guide to auto escorts at trainworld.us in the shipyard section.
Note there is no longer any costs for setting up or running auto escorts.

Here are some tips from my personal experience:
- Auto escorts are better suited to CV's
- If using one with BB, choose the smallest size ship for your escort, ie DD with most turrets,
and stay out of the way of large BB's on the line, as auto escorts buzz around getting in peoples way
- Remember to use the + button to stop escorts firing, you won't be very popular with your sides CV's
if your escort shoots down half of his planes, press + to resume firing
- Likewise if escort is using HE/AP, the dumb AI won't stop firing if a freindly ship gets in the line of fire
with an enemy
- If using CL/PCL as escort, put a Sonarman on its support slots to spot enemy subs
(FF's + DD's can spot subs without Sonarman)
- Equip escort with light engine, as they are usually too fast and continually zig zag to stay behind you
- Auto escorts work best with fastest gun sets, the AI is pretty dumb

Quenirland, you are way off.

The poster is asking about setting an actual Escort ship you can assign to your main ship. You are confusing that with the play style physically escorting another ship. see pic.

http://i40.tinypic.com/mv40eq.jpg

Quenirland, FYI, the frigate following my landing ship is an escort ship, the one this thread is concerning. It displays my name but I cannot control it. is automated to follow my main ship and fire on enemy ships/planes (depending on what I put on it) that comes in range.

This thread is asking about the specific details of the escort ship, not how to escort a fellow player in a battle.

On topic, some advanced details about the escorts are that they do not overheat so choose the engine with the highest cruise speed.

They also have 360 degrees of fire on all turrets, even the ones while facing the superstructure and can fire both R and T slots simultaneously.

They cannot fire at submerged submarines even if they see them with sonar. Needless to say they cannot operate torpedoes or DC. However they will fire at surfaced subs with HH. There have been situations where a surfaced sub sneaks up on a CV hanging in the back; the escort fires HH at the sub as it begins to dive and they explode while it is underwater, killing it.