IMO- Wheels are really a personal decision. No matter the style or size some will like them others not. I think the selection of 6 lug wheels is much better now than years ago. If you like any of the "stock" Chevy and Toyota wheels many will fit your truck if you want a stop gap until you decide. I have purchased "takeoffs" many times and got good wheels and tires. Check out the used Darrell Waltrip wheel from a Toyota tundra. (02-06 only).
The wheel size is the inner bead of the wheel not the outside rim measurement. say it is 20X7 - the rim outside measures about 21X7.5. (this really depends on the wheel as steel wheel are usually smaller than aluminum). Think about where the tire fits and that is the 20 inch diameter.
The second thing is tire size. A 205.70X15 is smaller in height/diameter than 225.75 X15. So it is possible to run a larger wheel with a shorter side wall and have virtually the same diameter. All depends on the look you want. It is a slippery slope
