6. Please give a detailed example of an attack against an enemy, as I didn't try it and am approximately clueless on how to achieve this. What is the goal: conquest of enemy planets, or ships, or simply destruction? Where and under what circumstances do the battles take place?
Well battles take place if you're at war with someone (or if 2 or more AI's are at war with each other).
If the AI declares war on you then you don't have a lot of choice.
But if you are the agressor then declaring war is simply up to your goals and what you want to do. What kind of victory do you want? Is it an advantage to you at the time. I learned this in my last game when the galaxy started going aflame in war and I didn't have planetary invasion tech yet. That really hurt me early on and I eventually got crushed.
I'll give you a quick example of my current game.
Tough or Crippling level (can't remember), large galaxy, 8 AI's, common habitable.
I was near the middle with the Drengin (ouch), Terrans to the right, Korx and Torians to the left, everyone else farther out.
Got a good start with 3 decent planets and a couple marginal. A minor was next to me as well a couple systems away that one of my marginals were in.
I'll get to the attacking. I made sure I got planetary invasion early on so I would be ready to take advantage of a situation. This allows me to invade planets with transports.
First invasion: The minor next to me had a juicy planet but I normally don't want to take over minors because they are good trading partners. They were between me and the Korx and the Korx declared war on them. Great, all I need to lose cultural control of that system. So I build a transport, send in 2 attack ships and declare war. Took the planet and that minor was done. It was a nice juicy class 16 planet anyway and the influence boost from it really pushed the Korx borders back.
Second invasion: I had found two nice planets on either side of the Drengin but they were "special" planets (heavy gravity and toxic). I traded around and researched to get both techs and settled immediately with my colony ships I had parked in each system.
So I had the Drengin partially surrounded and they only had 3 planets in their core area, 3 more scattered about. If you've played the game long enough you know the Drengin will eventually declare war on you. Here they are pretty weak. Large military for their size but I match that easily. I've got to take this chance to take them down before they rolled over someone. So I prepare by building up a couple extra fleets and transports. I declare war and move in and take their capital first. They fight back and I take heavy losses but hold. They quickly fell after that and I took all worlds but one that was too far away. They eventually surrendered to the Arceans.
3rd invasion: So now I control the entire center of the galaxy and much of the bottom. Korx at it again and they declared on the Torians. This made me take notice. Torians have hardly any military. Basically none. I don't need the Korx to double in size ether, they are strong enough. So despite the fact the Torians are my allies I can't allow someone else swallow them up. So I break my alliance and declare. I quickly move in with transports and fleets and take out what little resistance there is and take 5 of their planets with 4 turns. Their last planet they surrender to the Korx. But I got most of them first. I now control most of the bottom of the galaxy and my influence engulfs even the Korx home systems.
That's where I am at now. Basically I had to take advantage of the situations at hand. My goal is an alliance victory since I'm ally with 3 of those that are left but I won't let that sway me from battle again should it be best for me to do it. The Korx may need to die soon before they grow too strong.