Hey,
I haven't got Dark Game Studio, just DBPro, but I'm guessing you're taking about the DBPro interface when you say editor... Yep, you do need the editor to use Darkbasic pro, it's where you type your code and stuff

The DirectX error you're getting and the problem executing stuff is probably because Windows 8 doesn't come with DirectX 9 pre-installed. This should fix the problem:
http://www.microsoft.com/en-gb/download/details.aspx?id=35
I'm not sure about DarkAI and DarkLights... They should come with their own installer, so just run that, and it'll install the plugins to DBPro!
Treelife (TreeMagik?)is a separate program for making your own 3d trees and shrubs - you need to export the models when you're done, then load them into Darkbasic Pro! Probably best to try a few DBPro tutorials before you try doing that, though - it can be confusing if you don't know your way around the language already

Hope this helps, and good luck