Your English is miles ahead of my German, so don't be sorry.

1. Structures have very heavy armor. You are correct. Long range frigates (LRM, Illum, Assailants) don't get a bonus, but they aren't bad at it. They do 75% of their damage to structures, which isn't bad.

2. I'm not sure what you mean by defence platforms. If you mean turrets, they do no damage to SC. They do anti-medium damage.

If you mean the hangars (not sure if one of them is called the defence platform or not)

TEC Hangar: You can buy autocannon's for them. They do 40 dps per platform.

Advent Hangar: They can get 750 shields and regenerate 4 shield per second on it and every building around them.

Vasari Hangar: They can phase out enemy strikecraft for long periods of time. No damage done, but enemy loses use of those for some time.

3. SB have very heavy armor.....i think. I know bombers destroy them effectively, so I think they must have very heavy armor. I don't have access to the game right now, but my guess is Starbases do either starbase damage, or capital ship damage. I think starbases do 100% of their damage...regardless of the target. That's a guess.

4. You are correct. Be careful though. Light frigates take time to destroy carriers. You should use some flak too when going up against carriers. Those strikecraft can target stuff in the grav well after the carrier is dead.

Example: Enemy has 5 advent carriers (15 squads)

I'm TEC. I'll get 15 flak (1 flak per squadron), and then 8 cobalts OR 10 LRMS. I say 10 LRMS because once you destroy the strikecraft, you can jump in LRMS and they CAN chase down the carriers. Carriers are now slower than LRMS, and LRMS are much more useful than cobalts overall.

Cobalts WILL destroy the carrier faster than LRMS. They do anti-heavy damage, as you said. LRMS, however, will destroy anything else the enemy brings, cobalts most likely will not.

Carriers are a good option, but you may want to mix in some flak and lrfs. Flak DOMINATE hangar defenses and lrfs will protect them, and your carriers from light frigates, and they deal a decent damage percentage to buildings as well, speeding along their destruction.

As for taking out those fleets of caps and carriers, even a couple of illums can spell serious trouble for light frigates. I would recommend using bombers against enemy caps with some fighters to handle your opponent's, and some flak to help you dominate the skies. Flak take take a load of punishment from cap ships and keep chugging along. If you want to turn the tables even further build a fleet of lrfs, as they do a good damage percentage to cap ships as well, and your opponent will have to choose whether to go after your bombers or your lrfs.

You may also want to invest in Anti-Capital capital ships. Each race has one, for TEC its the Kol (which also has a very effective anti-SC ability). For advent, go with the Radiance, its detonate antimatter ability can prevent their cap ships from using their abilities, as well as their Guardians. For Vasari, the intended Cap ship killer is the Kortul, but in reality the Jarrasul evacuator is much more effective, as its Nano-dissasembler ability will chew right through those cap ships hulls and armor, dealing massive damage and allowing your ships to do more damage to them.

Cap Ship Killer + Flak + LRFs + Carriers = You win. Good luck.

1. The vasari LF is deceptively weak, early game, despite its health and firepower, it will be crushed by LRMs. However with reintegration technology, its a pretty good support cruiser hunter later in the game.

2. Hangar defenses are trouble for vasari sbs, you just have to make sure you dominate enemy SC before you start construction. Flak will help your fighters by keeping enemy fighters at bay.

1. Lfs biggest threats are Lrms and HCs

Right, without the support of LRMs and HCs, light frigates will be a serious threat to your opponents units. Also keep in mind that LFs are faster than LRMS. So if you can keep them away from the LRMS long enough to kill all or most of the LRMS you'll be in good shape.

Targeting Ai are a bit tricky, but here's what I know for sure:

Fighters will automatically target other SC over frigates (and don't have a preference for frigates), with bombers being their first priority and other fighters being their second. LRMS will auto target LFs most of the time. As far as I know LFs will just target anything, including the units designed to kill them. Flak will auto target enemy fighters as first priority and bombers as second. Scouts will choose not to autotarget anything. They prefer not to engage in battles but are surprisingly effective at killing LRFs (you just need a lot of them and have to do a little micro). HCs will target just about anything without preference (although HC militia favor your LRMS over everything else). Support cruisers also do not have a targeting preference when it comes to their weapons. And siege frigs will go after enemy planets.

Don't forget you can limit all this behavior by setting your units to hold position or local area only.