Hello Ur-Lugal,
Now, am I able to play a version with both add ons? Or do I have to choose between both addons DA or TotA??
you need to choose. Basically, these are 3 different games. They have alot in common - but they have also a lot of difference; ie. the way you play DL might not be possible in DA and so on...
So where is the difference, are both totally different games? Or does one addon contain the other? I want to play the game at it's best and dont want to miss some of the features ...
Personally I'd say - you start with DL, which has the basics which are also included in DA/TA. However, some stuff got nerfed in the expansions, namely ship-speed & diplomacy contact.
Then you go DA - which might be harder (because of the nerfs), and you got more stuff to micromanage, a few more techs and also SuperAbilities - which can change the play of a game very much.
This will leave you only TA - where each race has a unique Tech-tree - which makes it a game on its own.
and I'm a bit confused, i read something about "endless universe", so is it a third addon, contained in one of these 2 addons, or is it still in development and not released?
In "Endless Universe" are the same components as in the "Ultimate Edition". Concerning GalCiv2 - you have it complete if you have 1)DL 2)DA & 3)TA