I just made a non-combat thief. Who really only brawls from time to time. I had trouble with this type of character before as joining the thieves guild was hard as the rataway has hostile NPC's so I just gave myself the fence perk (how could merchants tell if something was stolen anyway) but I'm still not too knowledgable about what quests/content will be availuable to me now

Will I still be able to buy a house?

http://elderscrolls.wikia.com/wiki/Hjerim in Windhelm should be possible.

So the idea is I let the NPC's do all the fighting? (Never done the civil war quest line)

There are tricks to getting through the Rat Way without killing anyone. Arrows to distract, invisibility potions, the throw voice shout. Some of them you can just slip past in the dark if your stealth is high enough and your gear is quiet. Once you get accepted you won't need the Rat Way any more. There are a handful of places in the wilderness that you can sleep in that also have safe storage. I know one of them is a shack by a river just sw of Windhelm. More south than west though. No one is there so you don't have to kill anyone to move in except a bear maybe.