How many targets can the Kol attack at once? You just stated it can target only 1 still. I'm only playing the regular game right now (1.12 or whatever the current non-expansion beta is) but I can see it hit other targets from the sides once in a while. I guess those are the auto cannons.
It behaves exactly as it does in vanilla Sins. 
So are you saying you can *specify* multiple targets for a starbase to attack? You say 4 targets - that seems really low for starbase considering it sounds like a single bank can already hit 3 targets. I'm totally confused.
You can't specify them, it picks its own. You can specify the "primary" target like you do now when you right click, and it'll just pick 3 others. But think of it this way: in normal Sins (and the previous beta) each side could only hit one target. For example, the Kol's beams.. there are 4 beams that get fired, but it's one weapon and one shot. That's what the Starbase was doing. It had an ungodly number of firing points (8 for beams, probably over 20 for lasers) but it was always only attacking one target. Now it attacks 4. Same weapons, same firing points, it just looks a lot cooler because you have lasers and beams hitting different ships and all doing the same amount of damage. It's like in the movies where you see space stations firing every which way and blowing stuff up left and right 
Also - if you order a capital ship (Kol) to attack an enemy frigate will it turn to fire its beam weapon? And if that is the case - will it still continue to use its other weapons agains the surrounding ships in range?
Yes and yes.
And last question - where can we find information on banks and # of simultaneous targets for each ship?
As far as I know, the only things that can attack more than one target after this change are starbases and the Advent anti-structure cruisers. But it's not displayed anywhere in-game (yet, at least) so you have to dig in the files.
And do these ships have a "main" weapon that does more damage than the secondary weapons - which seems to be the case of the Kol.
Yes, the main weapon is always the one that does the most damage per side, not total. That's why the Kol's primary is the beam, even though the autocannon is listed as having higher DPS. The autocannon DPS is with all the sides added together, but each side on its own does lower damage than the beam.
If I target some fighters with the Kol for example what happens? Does it turn to chase them or do the side cannons attack them?
It can't attack fighters
