You've got a little bit of a can of worms here...but not too much.
Steering: You've changed the steering axis. In a sense, you've changed the relation to how far away the pivot is in relation to the outside of the tire. Think of it as a simple lever. The farther away from the pivot, the harder it will be to move. It'll cause a bit more strain on the steering components such as tie rods, gearbox, and your arms.....but it's nothing that should cause any damage. (unless you're worried about looking like popeye)
4 wheel drive:
This comes back to the general rule of "don't use it on hard surfaces". The front and rear wheels take a different track when you turn. So a bit of a "softer" surface is needed to allow for some slip between the front and rear end. If you widen the rear track, it becomes less of an issue, but just make sure that you keep it out of 4WD when you don't need it. That's the simplest solution.
Hopefully this all helps.
