I worked with AR through a local tire dealer. It was very easy. I researched a bit first to understand the pretty simple form you fill out and choose wheel style. Then worked with the dealer for a test wheel in standard BS and tire size I wanted for the front... then used that as reference for final measurements. Filled out the form with the dealer and ordered the 4 wheels/tires. In a couple weeks done. I bought the "measuring" wheel/tire as a spare.

On the 17's vs 18's it depends on what type of tire you want. There a lot of nice tires in 17's. If you go low profile ultra high performance, the 17's are a little short.