Let's say we're playing on a 40 planet galaxy and the player controls 35 of them. The wiki says that the AI won't get more than 15 reinforcement 'points', meaning he can only reinforce 15 planets max. In that case, it doesn't really matter that the player controls 35 as in the example or 15 as in a more realistic game, because the number of times he can reinforce is capped at 15. Does the danger of this, however, lie in the fact that instead of reinforcing 15 seperate planets a single time, he might now reinforce planets 3 times? I.e. tripling the number of reinforcements per planet?
Actually, I forgot about the 15 point cap -- so, no, it's 15 points total, regardless of how many planets (if one planet takes 3 points, then there's only 12 points left, etc). But, it still gets very challenging because the AIP is higher, and of course there's the time factor. If reinforcements are happening every 5-8 minutes or so (per AI player), and you've maxed out the reinforcement points, then that's a heck of a lot of ships getting added to the galaxy every 5-8 minutes. If it takes you even just 30 minutes to capture each planet, then after 5 hours of capturing an added 10 planets, the AIs have had (at worst) something like 1125 reinforcement points between the two of them. That's going to fill up quite a lot of planets, eh?
That time factor is actually the killer, it's going to be more and more of a slog if you just let the AI keep reinforcing constantly. If you strike quicker, there is less chance for the AI to do that.
Can the AI reinforce a planet more than 2 times (something which isn't implied on the wiki)?
Yes and no. Normally: no. The AI can double-reinforce planets that it is particularly worried about, but that's all. Beyond that, assuming that it has enough planets left to reinforce at, it will spread them out evenly unless there are other planets it is very worried about.
If not, then in the above case he would have 5 extra reinforcement points to spend. Will he add those reinforcements to the Threat level? I.e. Border aggression?
Here's where the yes comes in, from above. Assuming that the AI reaches the end of its list of planets and still has reinforcement points left, then it just goes through the whole loop again. Planets it's worried about probably get another double-dose, and so forth. If you've got the AI players down to a single planet, you're going to see 15x reinforcement points per AI player getting spent every 5-8 minutes. It's going to be a
bear of a battle.
Does border aggression only kick in when ALL planets are full? Because with the new stalking element, I doubt that there'd be many planets that have over 3500 ships, which is already a case where the AIP is 1200 according to the wiki. Even in my game I've never seen this (mostly due to the ships being in carriers and not counted towards the ship count in that planet).
No, it's per-planet. And the numbers on the wiki are actually only correct for High, the numbers are halved for Normal and quartered for Low ship caps. I'm sure you've seen border aggression, you just might not have known what it was, as it's pretty subtle: sometimes enemy ships show up, and it might not be clear why, but they always come from that giant heavily-reinforced planet over there, etc.
The wiki says that Border aggression means ships will start trickling into your system, won't they get added to Threat level instead? And only attack when the AI thinks he can beat you?
Yes, the wiki is referring to 4.021 and before, but now they act as you describe.
Will the AI prefer to double up (or triple up or ....) on alerted planets prior to reinforcing non-alerted planets? So, if there are three planets on alert and he has 6 reinforce points, will he first try to double up on all alerted planets and only if he can't choose a non-alerted planet to reinforce?
It depends. It evaluates each planet individually. If there are three planets on alert, and none of them are planets that the AI considers absolutely critical (it has its own non-visible internal evaluations for that), then it would just reinforce all three once, and then the other three would go somewhere random. If they were viewed as critical, then it would double them up. But simply being on alert at all doesn't have any bearing on if it will double them up.
Related to above questions: Can he triple up on 2 of the three planets instead of doubling up on all three?
Definitely he cannot.
If one of the homeworlds of the AI is destroyed, does this mean he can't reinforce anymore?
Destroying the homeworld of one AI has no effect on anything related to gameplay: you get nothing for it, and actually the AIP goes
up. This is the same on the human side in multiplayer: actually if one player loses their home planet, their economy gets
better. It's not until all the players on whichever team are dead that the game ends.
On the AI side, this prevents the game from being a downhill slide (as with most RTS games) after the first AI is dead. That's boring. And on the human side, this prevents co-op players from being out of the game early, and thus sitting around for a dozen hours with nothing to do (or, more likely, causing the entire team to give up or savescum as soon as one player loses their home).