You can run 20" wheels without any problems. Key is the offset for any wheel choice you decide. Now perfect offset for the 20x8.5" would be 15-22. For the 20x10.5" 15-22 as well. You shouldn't have any fitment problems or rubbing issues, especially in the front. Depending on your tire size in the rear, you may need to roll the fenders.
It seems the Tein Springs are the most commonly used. Just take into account that more than a 1" or so drop you may need to run adjustable camber components. I would suggest the Tein H techs, they give less of a drop than the S techs.
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