well, I currently own Vanilla+Entrenchment. I am planning on obtaining Diplo, and considering buying the Trinity pack.

The main thing is- if you're going to get all 3 at once, go with the Trinity pack, since it is cheaper than Vanilla+Entrench+Diplo or Bundle+Diplo.

yes. After the release of Diplo, there will be a retail box version that contains Sins+Entrenchment+Diplomacy. There is currently a retail version of vanilla Sins (just had to say as a backup plan, as I'm pretty sure everyone knows it) that is boxed, and you can have a retail box sent with the vanilla game's digital D/L.

On the neoseekers site IC said they were going to update the manual for Entrenchment and Diplomacy, but I'm sure that will be avaliable online. They might but some concept art in as well, but that's just a guess, from what we know its just a three in one package.