Advice needed: changing wheel and tire size.

I'm thinking of getting some winter tires. I have an 09 2LT w/18" wheels now. Whatever the stock tire size is. I don't have it handy. Perhaps one of you knows that and can post it. I'm likely going to go down in wheel size and up in sidewall size. 16 or 17 inch wheels (probably 16) should make tires easier to find and cheaper.

I know I need a 5x110 bolt pattern on the wheels, but how do I know what the width of the wheel and offset are? I never see that advertised. What's the width now and what width should I try to stay over/under for the wheel and the tire? What offset or range for offset should I look for? Can I get a large enough tire to comensate for the 2 inches in wheel size loss to prevent a speedometer innacuracy? Will that lare sidewall cause problems? Is the speedo difference that much anyway?

For those of you that have done this, what are some suggestions for wheel and tire sizes to look for?

Right now I'm looking at Blizzak ofr General Arctic tires.

Sorry for the number of questions and thanks for reading/helping.