The offset of the wheel refers to the location of the wheel mounting area. Here's a couple of references:
http://www.tirerack.com/wheels/tech/...jsp?techid=101
http://www.rsracing.com/tech-wheel.html
as far as steering/suspension components, imagine this. take a bar and add 45lb weights about 12" in on each side. twist it back and forth. now take those same weights and put them at the very ends of that bar and add 20lbs. you will find it takes more strength. by adding larger wheels/tires, you add weight and the offset puts the wheels out more. this all causes stress on any gears/moving parts of your suspension/steering.
BTW - Good choice on the wheels. Bigger fenders would eliminate the paint concers.
But that's a CLEAN ride! I don't remember it lifted in those pics you posted