Need help with wheels

[Travis K]

I need some advice. I would like to purchase my wheels and tires, so I can have a rolling chassis soon, but I am not sure what backspacing would be best for the wheels. I am going to be running 35x12.50R18 tires with a 4" lift (it's a street truck). Anyone have any advice for wheel width and backspacing? What is the backspacing on a stock wheel? One more questions: when I have been wheel shopping, some wheels list backspacing and offset. Can someone explain to me what offset is? it is usually listed in the 17-20mm range. Thanks for your help guys.