1. It's REALLY easy to bribe them into declaring war on another AI. If you make sure that all the other AIs are involved in at least 1 war at all times they will almost never declare war on you. It's almost essential to do this on maso/suicial.
Yeah, I agree. (I know, I know, this is going to sound like cheese) Typically, I try to have all AIs at war with all other AIs once they start wars on me. With nine opponents thats like 70 some wars going on at once. I do this because I noticed that when the AI is at war with multiple civs, it just keeps cranking out ships to fight, and doesn't build transports. You kind of "freeze" all the AIs in wars with each other, and just go around mopping up the stragglers.
Yes, this means you are at war with 6 or more people at once. And there is no trading for anybody. But really, with the new rules, it is much less intense to just send the whole galaxy up in flames fighting each other than to have to face 3 or more opponents on your own. If you can keep one civ not at war with you, you can trade peace treaties with other civs to them to control who you are even at war with.
2. The AI tends to strip a planet of defenses and then, several turns later, send in transports. This makes it really easy to swoop in and steal a planet from right under their noses.
I agree they don't defend planets they have just taken, so keep a transport in range of planets that have had the defenders destroyed. Rush buy transports with good speed and launch them if you think you will be conquered, this can be a good way to keep the planet and maybe even get a free tech off the offender.
I also continue to rape the tie rule when attacking planets that don't have an orbital fleet manager. In my last game (large galaxy, common settings all) I couldn't take out my enemies defenses when they were in fleets. So I went around and took all the AI planets without an OFM and tried to culture flip the ones with it, so I never had to waste fleets facing all that firepower. Especially bad were the arceans, who somehow managed medium hull frigates with 300 attack power. I just didn't want to fight a fleet with an attack power near 2k. But, one at a time, I only needed enough offense to take out the defense and 35 some hps that one ship carried in one round. Cake.