I killed Kolsc in my game, but it gave me an option to kill Raedric too. What would happen if I killed both of them?

Just save the game and try it. I guess every one in Gilded Vale will become hostile but i'am pretty sure you can play and complete the game without problems.

If the game give you the choice than you can do it.

it would be cool if your can take over Macbeth-style

Not.

You only get one keep and one land surrounding it. ;-)

yeah. i have my castle to set up. but it feels kind of ... what i mean is that it is a place outside the story and
it looks like they insert it random. only to have some kind of old jrpg over world.

p.s:
and i kill the whole population in the city! but then it quits some quests. is it possible to kill all the npcs?
i get some really nice amount of money. but when you go to a shop the things are to expensive!!